Pneumatic Tire

ABSTRACT

A pneumatic tire is provided with, in the tread surface, land portions that include a plurality of blocks. The land portions are provided with a plurality of narrow shallow grooves and a plurality of recessed portions in a contact patch. The opening area ratio Se′ of the recessed portions in the end portion regions in the tire circumferential direction of one continuous contact patch and the opening area ratio Sc′ of the recessed portions in the central portion region in the tire circumferential direction have the relationship Sc′&lt;Se′, where the central portion region is defined as the region in the central portion in the tire circumferential direction occupying 50% of the continuous contact patch, and the end portion regions are defined as the regions in the front and back end portions in the tire circumferential direction occupying 25%.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/529,067, filed on May 23, 2017, which is the National Stage ofInternational Patent Application No. PCT/JP2015/084062, filed on Dec. 3,2015, which claims the benefit of priority from Japan Patent ApplicationNo. 2014-245321, filed on Dec. 3, 2014 and Japan Patent Application No.2015-175793, filed on Sep. 7, 2015.

TECHNICAL FIELD

The present technology relates to a pneumatic tire and particularlyrelates to a pneumatic tire with improved braking performance on ice.

BACKGROUND ART

Typically, a new tire has chemicals adhered to the tread surface. Thesechemicals reduce the water absorbing function and edge function of theblocks in the early stages of wear, thus reducing the brakingperformance on ice.

Because of this, studless tires in recent years have been provided witha plurality of fine narrow shallow grooves in the surface of the blocks.In such a configuration, the narrow shallow grooves remove a film ofwater formed between the icy road surface and the tread surface in theearly stages of wear, thus improving the braking performance on ice ofthe tire. An example of a conventional pneumatic tire that is configuredin this manner is the technology described in Japanese Patent No.3702958B.

SUMMARY

The present technology provides a pneumatic tire with improved brakingperformance on ice.

An embodiment of the present technology is a pneumatic tire comprisingin a tread surface thereof a land portion that comprises a rib or aplurality of blocks,

the land portion comprising in a contact patch thereof a plurality ofnarrow shallow grooves and a plurality of recessed portions, and

-   -   an opening area ratio Se of the recessed portions in end portion        regions in a tire lateral direction of one continuous contact        patch in the land portion and an opening area ratio Sc of the        recessed portions in a central portion region in the tire        lateral direction having the relationship Sc<Se, where    -   the central portion region is defined as a region in a central        portion in the tire lateral direction occupying 50% of the        continuous contact patch, and the end portion regions are        defined as regions in left and right end portions in the tire        lateral direction occupying 25%.

Another embodiment of the present technology is a pneumatic tirecomprising in a tread surface thereof a land portion that comprises aplurality of blocks,

the land portion comprising in a contact patch thereof a plurality ofnarrow shallow grooves and a plurality of recessed portions, and

an opening area ratio Se′ of the recessed portions in end portionregions in a tire circumferential direction of one continuous contactpatch and an opening area ratio Sc′ of the recessed portions in acentral portion region in the tire circumferential direction having therelationship Sc′<Se′, where

the central portion region is defined as a region in a central portionin the tire circumferential direction occupying 50% of the continuouscontact patch, and the end portion regions are defined as regions infront and back end portions in the tire circumferential directionoccupying 25%.

According to a pneumatic tire according to an embodiment of the presenttechnology, the opening area ratio of the recessed portions is greaterin the end portion regions in the tire lateral direction or the tirecircumferential direction, which improves the water absorbency of theroad contact surface at the end portion regions where a film of water islikely to form. Such a configuration is beneficial because the groundcontact properties of the end portion regions are improved and brakingperformance on ice of the tire is improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of the presenttechnology.

FIG. 2 is a plan view illustrating a tread surface of the pneumatic tireillustrated in FIG. 1.

FIG. 3 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 2.

FIG. 4 is an enlarged view illustrating a main portion of a blockillustrated in FIG. 3.

FIG. 5 is a cross-sectional view of a contact patch of the blockillustrated in FIG. 4 taken along line A-A.

FIG. 6 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 2.

FIG. 7 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 2.

FIG. 8 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 9 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 10 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 11 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 12 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 13 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 14 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 15 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 16 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 17 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 5.

FIG. 18 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 19 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 20 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 21 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 4.

FIG. 22 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 2.

FIG. 23 is an explanatory diagram illustrating the modified example ofthe pneumatic tire illustrated in FIG. 2.

FIG. 24 is an explanatory diagram illustrating the modified example ofthe pneumatic tire illustrated in FIG. 2.

FIG. 25 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 2.

FIG. 26 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 25.

FIG. 27 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 25.

FIG. 28 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 25.

FIG. 29 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 25.

FIG. 30 is an explanatory diagram illustrating the modified example ofthe pneumatic tire illustrated in FIG. 25.

FIG. 31 is an explanatory diagram illustrating the modified example ofthe pneumatic tire illustrated in FIG. 25.

FIGS. 32A-32B include a table showing results of performance testing ofpneumatic tires according to embodiments of the present technology.

FIGS. 33A-33B include a table showing results of performance testing ofpneumatic tires according to embodiments of the present technology.

DETAILED DESCRIPTION

Embodiments of the present technology are described in detail below withreference to the drawings. However, the present technology is notlimited to these embodiments. Moreover, constituents of the embodimentsinclude elements that are replaceable while maintaining consistency withof the technology, and obviously replaceable elements. Furthermore, themodified examples described in the embodiments can be combined asdesired within the scope apparent to those skilled in the art.

Pneumatic Tire

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of the presenttechnology. The same drawing is a cross-sectional view illustrating aregion to one side in the tire radial direction. Also, the same drawingillustrates a radial tire for a passenger vehicle as an example of apneumatic tire.

In reference to the same drawing, “cross section in a tire meridiandirection” refers to a cross section of the tire taken along a planethat includes the tire rotation axis (not illustrated). Reference signCL denotes the tire equatorial plane and refers to a plane normal to thetire rotation axis that passes through the center point of the tire inthe tire rotation axis direction. “Tire lateral direction” refers to thedirection parallel with the tire rotation axis. “Tire radial direction”refers to the direction perpendicular to the tire rotation axis.

The pneumatic tire 1 has an annular structure with the tire rotationalaxis as its center and includes a pair of bead cores 11, 11, a pair ofbead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber15, a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers17, 17 (see FIG. 1).

The pair of bead cores 11, 11 are annular members constituted by aplurality of bead wires bundled together. The pair of bead cores 11, 11constitute the cores of the left and right bead portions. The pair ofbead fillers 12, 12 are disposed on peripheries of the pair of beadcores 11, 11 in the tire radial direction and constitute the beadportions.

The carcass layer 13 has a single-layer structure constituted by onecarcass ply or a multi-layer structure constituted by layered carcassplies, and stretches between the left and right bead cores 11, 11 in atoroidal form, forming the framework for the tire. Additionally, bothend portions of the carcass layer 13 are turned back outwardly in thetire lateral direction so as to wrap around the bead cores 11 and thebead fillers 12 and fixed. The carcass ply(plies) of the carcass layer13 is constituted by a plurality of carcass cords formed from steel oran organic fiber material (e.g. aramid, nylon, polyester, rayon, or thelike) covered by a coating rubber and subjected to a rolling process.The carcass ply(plies) has a carcass angle (inclination angle of thefiber direction of the carcass cords with respect to the tirecircumferential direction), as an absolute value, of from 80 degrees to95 degrees.

The belt layer 14 is formed by layering a pair of cross belts 141, 142and a belt cover 143 and is disposed around the periphery of the carcasslayer 13. The pair of cross belts 141, 142 are constituted by aplurality of belt cords formed from steel or an organic fiber materialcovered by coating rubber and subjected to a rolling process. The crossbelts 141, 142 have a belt angle, as an absolute value, of from 20degrees to 55 degrees. Furthermore, the pair of cross belts 141, 142have belt angles (inclination angle of the fiber direction of the beltcords with respect to the tire circumferential direction) of oppositesigns, and the belts are layered so that the fiber directions of thebelt cords intersect each other (crossply structure). The belt cover 143is constituted by a plurality of cords formed from steel or an organicfiber material covered by coating rubber and subjected to a rollingprocess. The belt cover 143 has a belt angle, as an absolute value, offrom 0 to 10 degrees. The belt cover 143 is disposed in a layered manneroutward of the cross belts 141, 142 in the tire radial direction.

The tread rubber 15 is disposed outward of the carcass layer 13 and thebelt layer 14 in the tire radial direction and constitutes a treadportion. The pair of sidewall rubbers 16, 16 are disposed outward of thecarcass layer 13 in the tire lateral direction and constitute left andright sidewall portions. The pair of rim cushion rubbers 17, 17 aredisposed inward of the left and right bead cores 11, 11 and the turnedback portions of the carcass layer 13 in the tire radial direction. Thepair of rim cushion rubbers 17, 17 constitute the contact surfaces ofthe left and right bead portions with the rim flanges.

Tread Pattern

FIG. 2 is a plan view illustrating a tread surface of the pneumatic tireillustrated in FIG. 1. The same drawing illustrates a tread pattern of astudless tire. In reference to the same drawing, “tire circumferentialdirection” refers to the direction revolving about the tire rotationalaxis. Reference sign T denotes a tire ground contact edge.

As illustrated in FIG. 2, the pneumatic tire 1 is provided with, in thetread portion, a plurality of circumferential main grooves 21, 22extending in the tire circumferential direction, a plurality of landportions 31 to 33 defined by the circumferential main grooves 21, 22,and a plurality of lug grooves 41 to 43 disposed in the land portions 31to 33.

“Circumferential main groove” refers to a circumferential groove with awear indicator that indicates the terminal stage of wear and typicallyhas a groove width of 5.0 mm or greater and a groove depth of 7.5 mm orgreater. Moreover, “lug groove” refers to a lateral groove having agroove width of 2.0 mm or greater and a groove depth of 3.0 mm orgreater.

The groove width is the maximum distance between the left and rightgroove walls at the groove opening portion and is measured when the tireis mounted on a specified rim, inflated to the specified internalpressure, and in an unloaded state. In configurations in which the landportions include notched portions or chamfered portions on the edgeportions thereof, the groove width is measured with reference to thepoints where the tread contact patch and extension lines of the groovewalls meet, when viewed in a cross-section normal to the groove lengthdirection. Additionally, in configuration in which the grooves extend ina zigzag-like or wave-like manner in the tire circumferential direction,the groove width is measured with reference to the center line of theamplitude of the groove walls.

The groove depth is the maximum distance from the tread contact patch tothe groove bottom and is measured when the tire is mounted on aspecified rim, inflated to the specified internal pressure, and in anunloaded state. Additionally, in configurations in which the groovesinclude an uneven portion or sipes on the groove bottom, the groovedepth is measured excluding these portions.

“Specified rim” refers to an “applicable rim” as defined by the JapanAutomobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim”as defined by the Tire and Rim Association, Inc. (TRA), or a “MeasuringRim” as defined by the European Tyre and Rim Technical Organisation(ETRTO). Additionally, “specified internal pressure” refers to a“maximum air pressure” as defined by JATMA, to the maximum value in“TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” as defined byTRA, and to “INFLATION PRESSURES” as defined by ETRTO. Additionally,“specified load” refers to a “maximum load capacity” as defined byJATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATIONPRESSURES” as defined by TRA, and a “LOAD CAPACITY” as defined by ETRTO.However, in the case of JATMA, for a passenger vehicle tire, thespecified internal pressure is an air pressure of 180 kPa, and thespecified load is 88% of the maximum load capacity.

For example, in the configuration of FIG. 2, four circumferential maingrooves 21, 22 having a straight shape are disposed having left-rightsymmetry about the tire equatorial plane CL. Additionally, five landportions 31 to 33 are defined by the four circumferential main grooves21, 22. The land portion 31 is disposed on the tire equatorial plane CL.The land portions 31 to 33 include a plurality of lug grooves 41 to 43disposed at predetermined pitches in the tire circumferential directionthat penetrate the land portions 31 to 33 in the tire lateral direction.The second land portions 32 are each provided with a circumferentialnarrow groove 23 that extends in the tire circumferential directionwhile bending. The land portions 31 to 33 are each formed as a row ofblocks that are defined by the circumferential main grooves 21, 22, thecircumferential narrow grooves 23, and the lug grooves 41 to 43.

Note that in the configuration of FIG. 2, as described above, thecircumferential main grooves 21, 22 have a straight shape. However, thepresent technology is not limited to such a configuration, and thecircumferential main grooves 21, 22 may have a zigzag shape or awave-like shape that bends or curves while extending in the tirecircumferential direction (not illustrated).

In the configuration of FIG. 2, as described above, the land portions 31to 33 are divided in the tire circumferential direction by the luggrooves 41 to 43, forming rows of blocks. However, the presenttechnology is not limited to such a configuration, and, for example, thelug grooves 41 to 43 may have a semi-closed structure in which the luggrooves 41 to 43 terminate within the land portions 31 to 33, thusforming the land portions 31 to 33 as ribs continuous in the tirecircumferential direction (not illustrated).

In the configuration of FIG. 2, the pneumatic tire 1 has a tread patternwith left-right symmetry. However, the present technology is not limitedto such a configuration, and, for example, the tread pattern may haveleft-right line symmetry, left-right asymmetry, or directionality in thetire rotation direction (not illustrated).

In the configuration of FIG. 2, the pneumatic tire 1 is provided withthe circumferential main grooves 21, 22 that extend in the tirecircumferential direction. However, the present technology is notlimited to such a configuration, and instead of the circumferential maingrooves 21, 22, the pneumatic tire 1 may be provided with a plurality ofinclined main grooves that extend while inclining at a predeterminedangle with respect to the tire circumferential direction. For example,the pneumatic tire 1 may be provided with a plurality of V-shapedinclined main grooves that have a V-shape projecting in the tirecircumferential direction and extend in the tire lateral directionopening to the left and right tread edges, a plurality of lug groovesthat connect adjacent V-shaped inclined main grooves, and a plurality ofland portions that are defined by the V-shaped inclined main grooves andthe lug grooves (not illustrated).

Block Sipes

FIG. 3 is an explanatory diagram illustrating a land portion of thepneumatic tire illustrated in FIG. 2. FIG. 3 is a plan view of one block5 that composes the shoulder land portion 33.

As illustrated in FIGS. 2 and 3, in the pneumatic tire 1, the blocks 5of the land portions 31 to 33 include a plurality of sipes 6. Byproviding the sipes 6, the edge components of the land portions 31 to 33increase and performance on snow and ice of the tire is improved.

Such a sipe is a cut formed in a land portion that typically has a sipewidth of less than 1.0 mm and a sipe depth of 2.0 mm or greater andcloses when the tire comes into contact with the ground. Note that themaximum value of the sipe depth is not particularly limited, but istypically less than the groove depth of the main grooves.

The sipe width is the maximum distance of the opening width of the sipeat the contact patch of the land portion and is measured when the tireis mounted on a specified rim, inflated to the specified internalpressure, and in an unloaded state.

Note that the sipes 6 may have a closed structure in which the sipes 6terminate within the land portions 31 to 33 at both end portions, asemi-closed structure in which the sipes 6 open at the edge portion ofthe block 5 at one end portion and terminate within the block 5 at theother end portion, or an open structure in which the sipes 6 open at theedge portions of the block 5 at both end portions. Additionally, thelength, number, and layout of the sipes 6 in the land portions 31 to 33can be appropriately selected within the scope apparent to those skilledin the art. The sipes 6 can extend in the tire lateral direction, thetire circumferential direction, or any direction inclined with respectto these directions.

For example, in the configuration of FIG. 3, the shoulder land portion33 includes the plurality of blocks 5 defined by the outermostcircumferential main groove 22 and the plurality of lug grooves 43 (seeFIG. 2). The blocks 5 each include a plurality of sipes 6. Additionally,the sipes 6 have a zigzag shape extending in the tire lateral direction,and are disposed side by side at predetermined pitches in the tirecircumferential direction. Additionally, the outermost sipes 6 in thetire circumferential direction has a closed structure in which the sipes6 terminate within the block 5 at both end portions. As a result, therigidity of the edge portions of the leading edge and the trailing edgeof the block 5 when the tire is rolling is ensured. The sipes 6 in thecentral portion in the tire circumferential direction have a semi-closedstructure in which the sipes 6 open to the circumferential main groove22 at one end portion and terminate within the block 5 at the other endportion. As a result, the rigidity of the block 5 in the central portiondecreases, and the stiffness distribution of the blocks in the tirecircumferential direction is made uniform.

Block Narrow Shallow Groove

FIG. 4 is an enlarged view illustrating a main portion of the blockillustrated in FIG. 3. FIG. 5 is a cross-sectional view of the contactpatch of the block illustrated in FIG. 4 taken along line A-A. FIG. 4illustrates the positional relationship between the sipes 6, narrowshallow grooves 7, and a recessed portion 8. FIG. 5 is a cross-sectionalview in the depth direction of the narrow shallow grooves 7 and therecessed portion 8.

In the pneumatic tire 1, the land portions 31 to 33 include a pluralityof narrow shallow grooves 7 in the contact patch (see FIG. 3). In such aconfiguration, by the narrow shallow grooves 7 taking in and removing afilm of water formed between an icy road surface and the tread surfacewhen the tire comes into contact with the ground, the brakingperformance on ice of the tire is improved.

The narrow shallow grooves 7 have a groove width of from 0.2 mm to 0.7mm and a groove depth Hg of from 0.2 mm to 0.7 mm (see FIG. 5). Thus,the narrow shallow grooves 7 are shallower than the sipes 6.Additionally, the narrow shallow grooves 7 are disposed across theentire surface of the land portions 31 to 33.

For example, in the configuration of FIG. 3, the narrow shallow grooves7 are disposed in the entire region of the contact patch of the shoulderland portion 33. The narrow shallow grooves 7 have a linear shape andare disposed at an incline of a predetermined inclination angle θ withrespect to the tire circumferential direction (see FIG. 4). The narrowshallow grooves 7 are disposed side by side at predetermined pitches P(see FIG. 4). As illustrated in FIG. 4, the narrow shallow grooves 7intersect the sipes 6 and are divided by the sipes 6 in the longitudinaldirection.

Note that as illustrated in FIG. 3, in a configuration in which thenarrow shallow grooves 7 are elongated and disposed side by side, a filmof water absorbed by the narrow shallow grooves 7 is guided through thenarrow shallow grooves 7 in the longitudinal direction and discharged.In such a configuration, the inclination angle θ of the narrow shallowgrooves 7 (see FIG. 4) is preferably in the range 20 degrees≤θ≤80degrees, and more preferably in the range 40 degrees≤θ≤60 degrees. Thedisposal pitch P (see FIG. 4) of the narrow shallow grooves 7 ispreferably in the range 0.5 mm<P<1.5 mm, and more preferably in therange 0.7 mm<P<1.2 mm. As a result, the film of water removing functionof the narrow shallow grooves 7 is appropriately ensured, and the groundcontact area of the land portions 31 to 33 is ensured. Note that thedisposal density of the narrow shallow grooves 7 is not particularlylimited but is constrained by the disposal pitch P described above.

The disposal pitch P of the narrow shallow grooves 7 is defined as thedistance between the groove center lines of adjacent narrow shallowgrooves 7, 7.

Block Recessed Portions

As illustrated in FIGS. 2 and 3, in the pneumatic tire 1, the landportions 31 to 33 each include a plurality of recessed portions 8 in thecontact patch. In such a configuration, by the recessed portions 8taking in a film of water formed between the icy road surface and thetread surface when the tire contacts the ground and the edge componentsof the land portions 31 to 33 being increased by providing the recessedportions 8, the braking performance on ice of the tire is improved.

Each of the recessed portions 8 is a closed recess (recess, or dimple,that does not open to the boundary of the contact patch) formed in thecontact patch of the land portions 31 to 33. The recessed portion 8 hasa discretionary geometrical shape at the contact patch of the landportions 31 to 33. For example, the shape of the recessed portion 8 maybe circular, elliptical, quadrangular, or another polygonal shape. Acircular or elliptical recessed portion 8 is preferable to reduce theuneven wear of the contact patch of the land portions 31 to 33, and apolygonal recessed portion 8 is preferable to improve the brakingperformance on ice via the increased edge components.

Additionally, the opening area of the recessed portion 8 preferablyranges from 2.5 mm² to 10 mm². For example, a circular recessed portion8 has a diameter ranging from approximately 1.8 mm to 3.6 mm. As aresult, the film of water removal performance of the recessed portion 8is ensured.

The opening area of the recessed portion 8 is the opening area of therecessed portion 8 at the contact patch of the land portions 31 to 33and is measured when the tire is mounted on a specified rim, inflated tothe specified internal pressure, and in an unloaded state.

Additionally, the depth Hd (see FIG. 5) of the recessed portion 8 andthe groove depth Hg of the narrow shallow groove 7 preferably have therelationship 0.5≤Hd/Hg≤1.5, and more preferably have the relationship0.8≤Hd/Hg≤1.2. In other words, the depth Hd of the recessed portion 8 isapproximately equal to the groove depth Hg of the narrow shallow groove7.

As a result, the water absorbing function of the contact patch of theland portions 31 to 33 is improved. Additionally, by the recessedportion 8 being shallow compared to the sipes (for example a linear sipe6 or a circular sipe (not illustrated)) the rigidity of the landportions 31 to 33 is appropriate ensured. Thus, the braking performanceon ice of the tire is ensured.

Additionally, a wall angle α (see FIG. 5) of the recessed portion 8 ispreferably in the range −85 degrees≤α≤95 degrees. In other words, theinner wall of the recessed portion 8 is preferably substantiallyvertical relative to the contact patch of the land portions 31 to 33. Asa result, the edge components of the recessed portion 8 are increased.

The wall angle α of the recessed portion 8 is the angle formed by thecontact patch of the land portions 31 to 33 and the inner wall of therecessed portion 8 when viewed in a depth direction cross-section of therecessed portion 8.

Additionally, as illustrated in FIG. 4, the recessed portion 8 isdisposed spaced apart from the sipes 6. In other words, the recessedportions 8 and the sipes 6 are disposed at different positions in thecontact patch of the land portions 31 to 33 and do not meet. Thedistance g between the recessed portion 8 and the sipes 6 is preferablyin the range 0.2 mm≤g, and more preferably in the range 0.3 mm≤g. As aresult, the rigidity of the land portions 31 to 33 is appropriatelyensured.

Additionally, as illustrated in FIG. 4, the recessed portion 8 isdisposed intersecting and communicating with the narrow shallow grooves7. The recessed portion 8 is disposed across separate adjacent narrowshallow grooves 7, 7. In other words, separate adjacent narrow shallowgrooves 7, 7 are disposed penetrating through one recessed portion 8. Asa result, the adjacent narrow shallow grooves 7, 7 communicate with eachother through the recessed portion 8. Additionally, the recessed portion8 is disposed between the adjacent narrow shallow grooves 7, 7 andpartially expands the volume of the narrow shallow grooves 7. Thus, whenthe tire comes into contact with the ground, water is retained in therecessed portion 8, and a film of water on the road contact surface isefficiently absorbed. As a result, the braking performance on ice of thetire is improved.

“Separate narrow shallow grooves 7” refers to a plurality of narrowshallow grooves 7 that extend without meeting in a pattern ofarrangement in which only the narrow shallow grooves 7 are present,excluding the sipes 6 and the recessed portions 8. Accordingly, noembodiments of the present technology have a pattern of arrangement inwhich the plurality of narrow shallow grooves 7 meet each other.

For example, in the configuration of FIG. 3, the narrow shallow grooves7 having a linear shape are disposed in the entire surface of the landportion 33 at predetermined pitches while inclining at a predeterminedangle with respect to the tire circumferential direction. As a result,as illustrated in FIG. 4, the adjacent narrow shallow grooves 7, 7 runside by side in the same direction. Additionally, the recessed portion 8is disposed across two adjacent narrow shallow grooves 7, 7 to allow thetwo adjacent shallow grooves 7, 7 to communicate with each other. Inother words, the two narrow shallow grooves 7, 7 running side by sidepenetrate through one recessed portion 8. Note that, the presenttechnology is not limited to the configuration described above, andthree or more narrow shallow grooves 7 may penetrate through onerecessed portion 8 (not illustrated).

Additionally, in the configuration described above, the number ofrecessed portions 8 disposed across the adjacent narrow shallow grooves7, 7 in the contact patch of one block 5 is preferably 70% or greater ofthe total number of recessed portions 8 in the contact patch, and morepreferably 80% or greater. As a result, the recessed portions 8 canfunction effectively to retain water as described above. For example, inthe configuration of FIG. 3, all of the recessed portions 8 are disposedacross two adjacent narrow shallow grooves 7, 7. However, the presenttechnology is not limited to such a configuration, and one or more ofthe recessed portions 8 may intersect with a single narrow shallowgroove 7 or be disposed between adjacent narrow shallow grooves 7, 7without intersecting a narrow shallow groove 7 (not illustrated).

Additionally, in the configuration of FIG. 3, the land portion 33 isprovided with the plurality of sipes 6 that define the narrow shallowgrooves 7 in the contact patch. Each section of the narrow shallowgrooves 7 defined by the sipes 6 extends without penetrating through aplurality of recessed portions 8. In other words, the recessed portions8 are disposed in a dispersed manner so that two or more recessedportions 8 are not disposed in the same section of the narrow shallowgrooves 7 defined by the sipes 6. Accordingly, in each section of thenarrow shallow grooves 7, a maximum of one recessed portion 8 isdisposed.

Additionally, as illustrated in FIG. 3, the recessed portions 8 are morethinly dispersed than the narrow shallow grooves 7. Specifically, thedisposal density Da of the recessed portions 8 in the entire region ofthe contact patch of one rib or block is preferably in the range 0.8unit/cm²≤Da≤4.0 unit/cm² and more preferably in the range 1.0unit/cm²≤Da≤3.0 unit/cm². As a result, the area of the contact patch ofthe land portions 31 to 33 is ensured.

The disposal density Da of the recessed portions 8 is defined as thetotal number of recessed portions 8 with respect to the area of thecontact patch of one rib or block. For example, in a configuration inwhich the land portions are ribs continuous in the tire circumferentialdirection (not illustrated), the total number of recessed portion 8 withrespect to the contact patch area of one entire rib is defined as thedisposal density Da. Alternatively, in a configuration in which the landportions are blocks (see FIGS. 2 and 3), the total number of recessedportions 8 with respect to the contact patch area of one block 5 isdefined as the disposal density Da.

The contact patch area is measured at a contact surface between a tireand a flat plate when the tire is mounted on a specified rim, inflatedto the specified internal pressure, placed vertically on the flat platein a static state, and loaded with a load corresponding to the specifiedload.

Recessed Portion Opening Area Ratio

In the pneumatic tire 1, the opening area ratio Se of the recessedportions 8 in the end portion regions ER (see FIG. 3) in the tirelateral direction defined at the continuous contact patch and theopening area ratio Sc of the recessed portions 8 in the central portionregion in the tire lateral direction have the relationship Sc<Se. Inother words, the opening area ratio Se of the recessed portions 8 in theend portion regions ER (see FIG. 3) is greater than that of the centralportion region. Additionally, the opening area ratios Se, Sc of therecessed portions 8 preferably have the relationship 1.50<Se/Sc, andmore preferably have the relationship 3.00<Se/Sc. The maximum value ofthe ratio Se/Sc is not particularly limited but is constrained by itsrelationship with, for example, the disposal density and opening area ofthe recessed portions 8. In a configuration in which all of the recessedportions 8 are disposed in the end portion regions ER (see, for example,the configuration of FIG. 7 described below), Sc is equal to zero, thussatisfying the condition Sc<Se.

The contact patch of the land portions is defined at a contact surfacebetween a tire and a flat plate when the tire is mounted on a specifiedrim, inflated to the specified internal pressure, placed vertically onthe flat plate in a static state, and loaded with a load correspondingto the specified load.

A continuous contact patch is defined as a contact patch defined bygrooves having a groove width of 2.0 mm or greater and a groove depth of3.0 mm or greater. Specifically, a contact patch of one rib or one blockdefined by lug grooves and circumferential grooves having the groovewidth and groove depth described above corresponds to the continuouscontact patch described above. Additionally, for example, closed luggrooves which terminate within the land portions, notches partiallyformed in the land portions (for example, notched portion 311 of FIG. 7described below), and sipes and kerfs that close when the tire comesinto contact with the ground do not divide the contact patch of the landportions, and thus do not correspond to the grooves described above.

The central portion region in the tire lateral direction is defined asthe region in the central portion occupying 50% of the continuouscontact patch in the tire lateral direction (see FIG. 3). The endportion region in the tire lateral direction is defined as the region ofthe left and right end portions each occupying 25% of the continuouscontact patch in the tire lateral direction. For example, in aconfiguration in which the land portions are ribs continuous in the tirecircumferential direction (not illustrated), the contact patch of oneentire rib is divided into the central portion region and the endportion regions in the tire lateral direction. Alternatively, in aconfiguration in which the land portions are rows of blocks (see FIG.2), the contact patch of each block that composes the row of blocks isdivided into a central portion region and end portion regions. Note thatthe dashed lines of FIG. 3 indicate the boundary lines between thecentral portion region and the end portion regions.

The opening area ratio of the recessed portions is defined as the ratiobetween the sum of the opening areas of the recessed portions disposedin a predetermined region and the contact patch area of the same region.In a configuration in which a recessed portion and a boundary line of aregion intersect, the recessed portion is considered to be disposed inthe region if its center point is within the region.

The opening area of the recessed portions and the contact patch area ofthe region are measured at a contact surface between a tire and a flatplate when the tire is mounted on a specified rim, inflated to thespecified internal pressure, placed vertically on the flat plate in astatic state, and loaded with a load corresponding to the specifiedload.

Additionally, in a configuration in which the land portions are formedby a plurality of blocks arranged in the tire circumferential direction(see FIG. 2), 70% or more, and preferably 80% or more of the blocks 5that compose one row of blocks preferably satisfy the condition Sc<Sefor the opening area ratio of the recessed portions 8 described above.In the entire tread, it is only required that at least one land portionsatisfy the conditions for the row of blocks described above.

The opening area ratio of the recessed portions 8 in the central portionregion and the end portion regions can be adjusted depending on thedisposal density of the recessed portions 8 in each region. In otherwords, by disposing the recessed portions 8 densely in the end portionregions ER in the tire lateral direction and sparsely in the centralportion region in the tire lateral direction, the opening area ratio Seof the recessed portions 8 in the end portion regions ER is madegreater.

Specifically, in reference to FIG. 3, by the disposal number Ne ofrecessed portions 8 in the end portion regions ER in the tire lateraldirection in one block 5 and the disposal number Nc of the recessedportions 8 in the central portion region (reference sign omitted in thedrawings) in the tire lateral direction having the relationship Nc<Ne,the condition Sc<Se for the opening area ratio of the recessed portions8 is satisfied. In other words, the recessed portions 8 are disposedunevenly in the contact patch of the one rib or one block so that thedisposal density of the recessed portions 8 in one rib or one blockdiffers between the end portion regions ER and the central portionregion in the tire lateral direction. Additionally, the disposal numbersNe, Nc of the recessed portions 8 preferably have the relationship1.50<Ne/Nc, and more preferably the relationship 3.00<Ne/Nc. The maximumvalue of the ratio Ne/Nc is not particularly limited but is constrainedby its relationship with the disposal density of the recessed portions8. In a configuration in which all of the recessed portions 8 aredisposed in the end portion regions ER (see, for example, theconfiguration of FIG. 7 described below), Nc is equal to zero, thussatisfying the conditions Sc<Se and Nc<Ne.

The disposal number of recessed portions is the number of recessedportions with their center points in the predetermined region.Accordingly, recessed portions that partially protrude from the regionare still considered to be disposed in the region if their center pointsare within the region.

Additionally, in a configuration in which the land portions are formedby a plurality of blocks arranged in the tire circumferential direction(see FIG. 2), 70% or more, and preferably 80% or more of the blocks 5that compose one row of blocks preferably satisfy the condition Nc<Nefor the disposal number of the recessed portions 8 described above. Inthe entire tread, it is only required that at least one land portionsatisfy the conditions for the row of blocks.

Note that as described above, because the central portion region of theblock 5 is defined as the region of the central portion occupying 50% ofthe contact patch of the block 5, in one block 5, the contact patch areaof the central portion region and the contact patch area of the endportion regions are essentially equal excluding any notched portions andnarrow grooves. As a result, in a configuration in which each recessedportion 8 of the block 5 has the same opening area, because of thecondition Nc<Ne of the disposal numbers of the recessed portions 8described above, the sum of the opening areas of the recessed portions 8in the end portion regions is greater than the sum of the opening areasof the recessed portions 8 in the central portion region.

In the configuration described above, the recessed portions 8 aredisposed densely in the end portion regions ER of the blocks 5 where afilm of water is likely to form. Thus, a film of water on the roadcontact surface is efficiently absorbed due to the water absorbingfunction provided by the recessed portions 8. As a result, the adhesiveproperties of the block road contact surface to an icy road surface isimproved, and the braking performance on ice of the tire is improved.Additionally, by disposing the recessed portions 8 sparsely in thecentral portion region, the contact patch area of the central portionregion of the block 5 is ensured and the braking performance on ice ofthe tire is improved.

In particular, the shoulder land portions 33 (defined as the laterallyouter land portions defined by the outermost circumferential maingrooves) have a great effect on braking performance of the tire. Thus,as illustrated in FIG. 3, by the recessed portions 8 being denselydisposed in the end portion regions ER in the tire lateral direction ofthe block 5 of the shoulder land portion 33, the function of therecessed portions 8 to improve braking performance on ice issignificantly obtained.

For example, in the configuration of FIG. 3, one block 5 of the shoulderland portion 33 includes a total of eleven recessed portions 8 in thecontact patch. Specifically, a total of eight recessed portions 8 aredisposed in the left and right end portion regions ER, ER in the tirelateral direction of the contact patch and a total of three recessedportions 8 are disposed in the central portion region. Additionally, therecessed portions 8 have the same opening shape and the same openingarea. The disposal number Ne of the recessed portions 8 in the endportion regions ER in the tire lateral direction and the disposal numberNc of the recessed portions 8 in the central portion region in the tirelateral direction have the relationship Ne/Nc=8/3=2.67. Additionally,all of the recessed portions 8 of the blocks 5 in the entire shoulderland portion 33 satisfy the condition for the disposal number Nedescribed above (see FIG. 2).

In the configuration of FIG. 3, the blocks 5 of the shoulder landportion 33 include a rectangular contact patch. The sipes 6 are disposedside by side in the tire circumferential direction and divide the blocks5 into a plurality of sections in the tire circumferential direction.Each section includes at least one recessed portion 8. In the section inthe central portion of the block 5 in the tire circumferentialdirection, the section including the recessed portion 8 in the endportion of the block 5 proximal to the circumferential main groove 22and the section without a recessed portion 8 in this end portion aredisposed in an alternating arrangement in the tire circumferentialdirection. In the sections in both end portions of the block 5 in thetire circumferential direction, the recessed portions 8 are disposed inthe corner portions of the block 5 proximal to the circumferential maingroove 22. In the sections in both end portions of the block 5 in thetire circumferential direction, the recessed portions 8 are disposedonly in the corner portions and are not disposed in the central portionregion in the tire lateral direction.

Corner portions of the land portions 31 to 33 are defined as the regions5 mm square including the corner portion of the contact patch of theland portion. The corner portion of the land portion is not just theportion of the land portion defined by the main groove and the luggroove, but also includes the portion of the land portion defined by anotched portion (for example, a notched portion 311 of FIG. 7 describedbelow) formed in the land portion. Additionally, the recessed portion 8is considered to be disposed in the corner portion described above ifthe center of the recessed portion 8 is in the corner portion.

In the configuration of FIG. 3, three discretionary adjacent sections inthe tire circumferential direction include a section including arecessed portion 8 in the end portion regions ER in the tire lateraldirection and a section including a recessed portion 8 in the centralportion region in the tire lateral direction. As a result, the recessedportions 8 are disposed dispersedly throughout the end portion regionsER and the central portion regions of the land portions 31 to 33.

“Sections in both end portions of the block 5 in the tirecircumferential direction” refer to a pair of sections located at bothend portions in the tire circumferential direction of the sections ofthe block 5 defined by the sipes 6 in the tire circumferentialdirection. “Section in the central portion of the block 5 in the tirecircumferential direction” refers to the section excluding the sectionsin both end portions in the tire circumferential direction.

When the tire comes into contact with the ground, ground contactpressure acts upon the end portion region ER of the block 5 in the tirelateral direction, in particular the end portion region ER proximal tothe circumferential main groove 22 and the corner portions, more thanthe central portion of the block 5. As a result, during travel on icyroad surfaces, the ice on the road surface is readily melted by theground contact pressure and forms a film of water. Accordingly, bydisposing the recessed portions 8 in the end portion region ER and thecorner portions of the blocks 5, the film of water on the road contactsurface is efficiently absorbed, and the braking performance on ice ofthe tire is improved.

Additionally, in the configuration of FIG. 3, the sipes 6 are disposedparallel with or at a slight incline to the lug grooves 43. The sipes 6are also disposed only in the region inward from the tire ground contactedge T in the tire lateral direction. The narrow shallow grooves 7extend beyond the tire ground contact edge T to the outer region of theland portion 33 in the tire lateral direction. The recessed portions 8are disposed only in the region inward from the tire ground contact edgeT in the tire lateral direction.

“Tire ground contact edge T” refers to the maximum width position in thetire axial direction of the contact surface between the tire and a flatplate and is measured when the tire is mounted on a specified rim,inflated to the specified internal pressure, placed vertically on theflat plate in a static state, and loaded with a load corresponding tothe specified load.

FIGS. 6 and 7 are explanatory diagrams illustrating the land portions ofthe pneumatic tire illustrated in FIG. 2. FIG. 6 is a plan view of oneof the blocks 5 that compose the second land portion 32. FIG. 7 is aplan view of one of the blocks 5 that compose the center land portion31.

In the configuration of FIG. 2, the second land portions 32 are eachdivided in the tire lateral direction by one circumferential narrowgroove 23 and further divided in the tire circumferential direction by aplurality of lug grooves 42, which forms a plurality of blocks 5.Additionally, in the inner region of each of the second land portions 32in the tire lateral direction, blocks 5 longer in the tirecircumferential direction are formed, and in the outer region in thetire lateral direction, shorter blocks 5 are formed. Note that thesecond land portion 32 is defined as an inner land portion in the tirelateral direction defined by the outermost circumferential main groove22.

Additionally, as illustrated in FIG. 6, one block 5 of the second landportion 32 located outward in the tire lateral direction includes arectangular contact patch. The sipes 6 are disposed side by side in thetire circumferential direction to divide the block 5 into a plurality ofsections. Each section includes at least one recessed portion 8.Additionally, sections in the central portion of the block 5 in the tirecircumferential direction (the sections excluding the sections in bothend portions in the tire circumferential direction) have an arrangementin which sections including the recessed portions 8 only in the endportion regions ER of the block 5 in the tire lateral direction and thesections including the recessed portions 8 only in the central portionregion in the tire lateral direction are disposed alternately in thetire circumferential direction. In the sections in both end portions ofthe block 5 in the tire circumferential direction, the recessed portions8 are disposed in the four corner portions of the block 5 and are notdisposed in the central portion region in the tire lateral direction.

Additionally, one block 5 includes a total of ten recessed portions 8 inthe contact patch. Specifically, a total of eight recessed portions 8are disposed in the left and right end portion regions ER in the tirelateral direction and two recessed portions 8 are disposed in thecentral portion region in the tire lateral direction. Additionally, therecessed portions 8 have the same opening shape and the same openingarea. The disposal number Ne of the recessed portions 8 in the endportion regions ER of the block 5 in the tire lateral direction and thedisposal number Nc of the recessed portions 8 in the central portionregion (reference sign omitted in the drawings) in the tire lateraldirection have the relationship Ne/Nc=8/2=4.00. Additionally, in thesecond land portion 32, the recessed portions 8 in all of the blocks 5satisfy the condition Nc<Ne described above (see FIG. 2).

Typically, in the land portion 32 including the shorter blocks 5, therigidity of the blocks 5 is reduced, thus when the vehicle brakes, theamount the blocks 5 collapse is great. In particular, in a configurationin which the blocks 5 include a plurality of sipes 6, this tendency issignificant and the braking performance on ice of the tire issusceptible to being decreased. However, in such a configuration, by theblocks 5 being provided with the recessed portions 8 in all of thesections of the block 5 defined by the sipes 6, a film of water on theroad contact surface is efficiently absorbed, and the brakingperformance on ice of the tire is ensured.

In particular, the second land portions 32 have a great effect on thedriving/braking performance of the tire. Thus, as illustrated in FIG. 6,by the recessed portions 8 being densely disposed in the end portionregions ER in the tire lateral direction of the block 5 of the secondland portion 32, a film of water can be efficiently absorbed at the endportion regions ER where a film of water is likely to form, and thefunction of the recessed portions 8 to improve braking performance onice is significantly obtained.

In the configuration of FIG. 2, the center land portion 31 is divided inthe tire circumferential direction by a plurality of lug grooves 41 intoa plurality of blocks 5. Additionally, the blocks 5 include notchedportions 311 on extension lines of the lug grooves 42 of the second landportion 32. The blocks 5 include a rectangular contact patch. Note thatthe center land portion is defined as the land portion 31 on the tireequatorial plane CL (see FIG. 2) or adjacent land portions on eitherside of the tire equatorial plane CL (not illustrated).

Additionally, as illustrated in FIG. 7, the sipes 6 are disposed side byside in the tire circumferential direction to divide the block 5 into aplurality of sections. The block 5 includes sections without a recessedportion 8. Three discretionary adjacent sections include a sectionwithout a recessed portion 8. For example, in the configuration of FIG.7, the section including the recessed portion 8 in only both endportions of the block 5 in the tire lateral direction and the sectionwithout a recessed portion 8 are disposed in an alternating arrangementin the tire circumferential direction. Additionally, the recessedportions 8 are disposed in the four corner portions of the block 5. Inthe sections in both end portions of the block 5 in the tirecircumferential direction, the recessed portions 8 are disposed only inthe corner portions of the block 5 and are not disposed in the centralportion region in the tire lateral direction.

Additionally, the section including the notched portion 311 includes therecessed portion 8 in close proximity to the notched portion 311.

The disposal number Ne of the recessed portions 8 in the end portionregions ER of the block 5 in the tire lateral direction is 18, and thedisposal number Nc of the recessed portions 8 in the central portionregion in the tire lateral direction is zero. Additionally, the recessedportions 8 have the same opening shape and the same opening area.Additionally, in the center land portion 31, the recessed portions 8 inall of the blocks 5 satisfy the condition Nc<Ne described above (seeFIG. 2).

Typically, the center land portion 31 preferably has high rigidity toensure the steering stability performance of the tire. Thus, asillustrated in FIG. 7, by the blocks 5 of the center land portion 31being partially provided with sections without a recessed portion 8, therigidity of the blocks 5 is ensured, and the steering stabilityperformance of the tire is ensured.

Additionally, the center land portion 31 has a great effect on thedriving performance of the tire. Thus, as illustrated in FIG. 7, by therecessed portions 8 being densely disposed in the end portion regions ERin the tire lateral direction of the block 5 of the center land portion31, the edge components are increased, and driving performance isimproved.

Note that in the configuration described above, at least one recessedportion 8 is preferably disposed in a position that corresponds to avent hole of the tire mold (not illustrated). In other words, in thevulcanization molding of the tire, because the green tire is pressedagainst the tire mold, the air in the tire mold needs to be dischargedoutside. Accordingly, the tire mold includes a plurality of vent devices(not illustrated) in the mold surface for forming the contact patch ofthe land portions 31 to 33. Additionally, one type of vent device formsa vent hole (small recess) in the mold surface corresponding to thepost-vulcanization land portions 31 to 33. Thus, by using the vent holeas a recessed portion 8, the vent hole is effectively utilized, and thenumber of unnecessary recesses are reduced in the contact patch of theland portions 31 to 33 allowing the contact patch area of the landportions 31 to 33 to be appropriately ensured.

First Modified Example

FIGS. 8 to 14 are explanatory diagrams illustrating modified examples ofthe pneumatic tire illustrated in FIG. 4. These drawings illustrate thepositional relationship between the sipes 6, the narrow shallow grooves7, and the recessed portion 8.

In the configuration of FIG. 4, the narrow shallow grooves 7 aredisposed at an incline of a predetermined angle θ with respect to thetire circumferential direction. Such a configuration is preferablebecause the inclined narrow shallow grooves 7 provide edge components inboth the tire circumferential direction and the tire lateral direction.

However, the present technology is not limited to such a configuration,and the narrow shallow grooves 7 may extend parallel with the tirecircumferential direction (see FIG. 8), or may extend parallel with thetire lateral direction (see FIG. 9).

Additionally, in the configuration of FIG. 4, the narrow shallow grooves7 have a linear shape. Such a configuration is preferable because thenarrow shallow grooves 7 are easily formed.

However, the present technology is not limited to such a configuration,and the narrow shallow grooves 7 may have a zigzag shape (see FIG. 10),or a wave-like shape (see FIG. 11). In such configurations, asillustrated in FIGS. 10 and 11, the plurality of narrow shallow grooves7 may be disposed in phase with each other, or as illustrated in FIG.12, may be disposed out of phase with each other. Additionally, asillustrated in FIG. 13, the narrow shallow grooves 7 may have a bent orcurved short structure. In such configurations, the short narrow shallowgrooves 7 may be arranged in rows offset from each other (see FIG. 13),or may be disposed arranged in a matrix (not illustrated). Additionally,the narrow shallow grooves 7 may have an arc shape (see FIG. 14), or mayhave a curved shape like an S-shape (not illustrated).

In the configurations of FIGS. 10 to 14, in a manner similar to that ofthe configurations of FIGS. 4, 8, and 9, the narrow shallow grooves 7may incline at a predetermined angle θ with respect to the tirecircumferential direction, may extend parallel with the tirecircumferential direction, or may extend parallel with the tire lateraldirection. Note that in configurations in which the narrow shallowgrooves 7 have a zigzag shape or a wave-like shape, the inclinationangle θ of the narrow shallow grooves 7 is measured with reference tothe center of the amplitude of the zigzag shape or the wave-like shape.

FIGS. 15 and 16 are explanatory diagrams of modified examples of thepneumatic tire illustrated in FIG. 4. These drawings illustrate thepositional relationship between the sipes 6, the narrow shallow grooves7, and the recessed portion 8.

In the configuration of FIG. 4, the narrow shallow grooves 7 have alinear structure that extends in a predetermined direction. Such aconfiguration is preferable because the narrow shallow grooves 7 canextend continuously throughout the entire region of the contact patch ofthe blocks 5.

However, the present technology is not limited to such a configuration,and as illustrated in FIGS. 15 and 16, the narrow shallow grooves 7 mayhave an annular structure and be disposed at predetermined pitches fromeach other. For example, the shape of the narrow shallow grooves 7 maybe circular (FIG. 15), elliptical (not illustrated), or rectangular(FIG. 16), triangular, hexagonal, or another polygonal shape (notillustrated). In such a configuration also, the recessed portion 8 isdisposed across separate adjacent narrow shallow grooves 7, 7.

FIG. 17 is an explanatory diagram illustrating a modified example of thepneumatic tire illustrated in FIG. 5. The same drawing illustrates across-sectional view of narrow shallow grooves 7 a, 7 b and the recessedportion 8 in the depth direction.

In the configuration of FIG. 5, all of the narrow shallow grooves 7 havethe same groove depth Hg.

Alternatively, in the configuration of FIG. 17, the groove depth of atleast one of the narrow shallow grooves 7 b is lower than the standardgroove depth Hg of the narrow shallow groove 7 a. In such aconfiguration, when tire wear advances, the narrow shallow grooves 7 bwith a lower groove depth disappear first. The narrow shallow grooves 7a with the greater groove depth Hg disappear thereafter. Thisconfiguration can suppress a change in the properties of the blocks 5that is caused by simultaneous disappearance of all of the narrowshallow grooves 7.

FIGS. 18 to 21 are explanatory diagrams illustrated modified examples ofthe pneumatic tire illustrated in FIG. 4. These drawings illustrate thepositional relationship between the sipes 6, the narrow shallow grooves7, and the recessed portion 8.

In the configuration of FIG. 4, all of the narrow shallow grooves 7 aredisposed in parallel with each other. As a result, the narrow shallowgrooves 7 are disposed in a stripe-like manner in which the narrowshallow grooves 7 do not intersect with each other.

However, the present technology is not limited to such a configuration,and as illustrated in FIGS. 18 to 21, the narrow shallow grooves 7 maybe disposed intersecting each other or communicating with each other.For example, as illustrated in FIGS. 18 and 19, the plurality of narrowshallow grooves 7 are disposed in a mesh-like manner. In such aconfiguration, the narrow shallow grooves 7 may be disposed at anincline with respect to the tire circumferential direction and the tirelateral direction (see FIG. 18) or disposed in parallel with the tirecircumferential direction and the tire lateral direction (see FIG. 19).Additionally, at least one of the narrow shallow grooves 7, for example,may be disposed in an arc-like or wave-like curving manner (see FIG.20). Additionally, the narrow shallow grooves 7 may have an annularstructure and be disposed communicating with each other (FIG. 21). Forexample, in the configuration of FIG. 21, the narrow shallow grooves 7are disposed in a honeycomb-like manner. Additionally, in theseconfigurations, the recessed portion 8 is disposed intersecting two ormore narrow shallow grooves 7 that do not intersect each other.

Second Modified Example

FIGS. 22 to 24 are explanatory diagrams illustrating a modified exampleof the pneumatic tire illustrated in FIG. 2. FIG. 22 is a plan view ofone of the blocks 5 that compose the shoulder land portion 33. FIG. 23is a plan view of one of the blocks 5 that compose the second landportion 32. FIG. 24 is a plan view of one of the blocks 5 that composethe center land portion 31.

In the configuration of FIG. 2, the plurality of recessed portions 8 aredisposed unevenly in the continuous contact patch of one block 5 sothat, as defined above for the continuous contact patch, the openingarea ratio Se of the recessed portions 8 in the end portion regions ERin the tire lateral direction is greater than the opening area ratio Scof the recessed portions 8 in the central portion region in the tirelateral direction (Sc<Se). Specifically, as illustrated in FIGS. 3, 6,and 7, all of the block 5 of the land portions 31 to 33 have therelationship Nc<Ne, wherein Ne is the disposal number of recessedportions 8 in the end portion regions ER in the tire lateral directionand Nc is the disposal number of recessed portions 8 in the centralportion region in the tire lateral direction.

Alternatively, in the modified examples of FIGS. 22 to 24, the openingarea ratio Se′ of the recessed portions 8 in the end portion regions ER′in the tire circumferential direction defined at the continuous contactpatch and the opening area ratio Sc′ of the recessed portions 8 in thecentral portion region in the tire circumferential direction have therelationship Sc′<Se′. Additionally, the opening area ratios Se′, Sc′ ofthe recessed portions 8 preferably have the relationship 1.50<Se′/Sc′,and more preferably have the relationship 3.00<Se′/Sc′. The maximumvalue of the ratio Se′/Sc′ is not particularly limited but isconstrained by its relationship with the disposal density and openingarea of the recessed portions 8. In a configuration in which all of therecessed portions 8 are disposed in the end portion regions ER′, Sc′ isequal to zero, thus satisfying the condition Sc′<Se′.

The central portion region in the tire circumferential direction isdefined as the region in the central portion occupying 50% of thecontinuous contact patch in the tire circumferential direction (see FIG.22). The end portion region in the tire circumferential direction isdefined as the region of the front and back end portions each occupying25% of the continuous contact patch in the tire circumferentialdirection. The central portion region and the end portion regions aredefined excluding notched portions partially formed in the land portions31 to 33. Additionally, the contact patch of each block 5 that composesthe row of blocks is divided into a central portion region and endportion regions. Note that the dashed lines of FIG. 22 indicate theboundary lines between the central portion region and the end portionregions.

Specifically, in reference to FIGS. 22 to 24, by the disposal number Ne′of recessed portions 8 in the end portion regions ER′ in the tirecircumferential direction in one block 5 and the disposal number Nc′ ofthe recessed portions 8 in the central portion region in the tirecircumferential direction having the relationship Nc′<Ne′, the conditionSc′<Se′ for the opening area ratio of the recessed portions 8 issatisfied. Additionally, the disposal numbers Ne′, Nc′ of the recessedportions 8 preferably have the relationship 1.50<Ne′/Nc′, and morepreferably the relationship 3.00<Ne′/Nc′. The maximum value of the ratioNe′/Nc′ is not particularly limited but is constrained by itsrelationship with the disposal density of the recessed portions 8. In aconfiguration in which all of the recessed portions 8 are disposed inthe end portion regions ER′, Nc′ is equal to zero, thus satisfying theconditions Nc′<Ne′ and Sc′<Se′.

Additionally, in a configuration in which the land portions are formedby a plurality of blocks arranged in the tire circumferential direction(see FIG. 2), 70% or more, and preferably 80% or more of the blocks 5that compose one row of blocks preferably satisfy the conditions Nc′<Ne′and Sc′<Se′ for the recessed portions 8 described above. In the entiretread, it is only required that at least one land portion satisfies theconditions for the row of blocks.

In the configuration described above, the recessed portions 8 aredisposed densely in the end portion regions ER′ of the blocks 5 where afilm of water is likely to form. Thus, a film of water on the roadcontact surface with an icy road surface is efficiently absorbed due tothe water absorbing function provided by the recessed portions 8. As aresult, the adhesive properties of the block road contact surface to anicy road surface is improved, and the braking performance on ice of thetire is improved. Additionally, by disposing the recessed portions 8sparsely in the central portion region, the contact patch area of thecentral portion region of the block 5 is ensured and the brakingperformance on ice of the tire is improved.

For example, in the configuration of FIG. 22, one block 5 of theshoulder land portion 33 includes a total of 13 recessed portion 8 inthe contact patch. Specifically, a total of eight recessed portions 8are disposed in the front and back end portion regions ER′ in the tirecircumferential direction and five recessed portions 8 are disposed inthe central portion region (reference sign is omitted in the drawings)in the tire circumferential direction. Additionally, the recessedportions 8 have the same opening shape and the same opening area. Thedisposal number Ne′ of the recessed portions 8 in the end portionregions ER′ in the tire circumferential direction and the disposalnumber Nc′ of the recessed portions 8 in the central portion region inthe tire circumferential direction have the relationshipNe′/Nc′=8/5=1.60. Additionally, in one of the shoulder land portions 33,all of the recessed portions 8 of the blocks 5 satisfy the conditionNc′<Ne′ described above.

In particular, the shoulder land portions 33 have a great effect on thebraking performance of the tire. Thus, by the recessed portions 8 beingdensely disposed in the end portion regions ER′ in the tirecircumferential direction of the block 5 of the shoulder land portion33, the function of the recessed portions 8 to improve brakingperformance on ice is significantly obtained.

Additionally, in the configuration of FIG. 23, one block 5 of the secondland portion 32 located outward in the tire lateral direction (see FIG.2) includes a total of nine recessed portion 8 in the contact patch.Specifically, a total of six recessed portions 8 are disposed in thefront and back end portion regions ER′ in the tire circumferentialdirection and three recessed portions 8 are disposed in the centralportion region (reference sign is omitted in the drawings) in the tirecircumferential direction. Additionally, the recessed portions 8 havethe same opening shape and the same opening area. The disposal numberNe′ of the recessed portions 8 in the end portion regions ER′ of theblock 5 in the tire circumferential direction and the disposal numberNc′ of the recessed portions 8 in the central portion region in the tirecircumferential direction have the relationship Ne′/Nc′=6/3=2.00.Additionally, in one of the second land portions 32, all of the recessedportions 8 of the blocks 5 satisfy the condition Nc′<Ne′ describedabove.

In particular, the second land portions 32 have a great effect on thedriving/braking performance of the tire. Thus, by the recessed portions8 being densely disposed in the end portion regions ER′ in the tirecircumferential direction of the block 5 of the second land portion 32,a film of water can be efficiently absorbed at the end portion regionsER′ where a film of water is likely to form, and the function of therecessed portions 8 to improve braking performance on ice issignificantly obtained.

Additionally, in the configuration of FIG. 24, one block 5 of the centerland portion 31 includes a total of 22 recessed portion 8 in the contactpatch. Specifically, a total of 13 recessed portions 8 are disposed inthe front and back end portion regions ER′ in the tire circumferentialdirection and nine recessed portions 8 are disposed in the centralportion region (reference sign is omitted in the drawings) in the tirecircumferential direction. Additionally, the recessed portions 8 havethe same opening shape and the same opening area. The disposal numberNe′ of the recessed portions 8 in the end portion regions ER′ in thetire circumferential direction and the disposal number Nc′ of therecessed portions 8 in the central portion region in the tirecircumferential direction have the relationship Ne′/Nc′=13/9=1.44.Additionally, in one of the center land portions 31, all of the recessedportions 8 of the blocks 5 satisfy the condition Nc′<Ne′ describedabove.

In particular, the center land portion 31 has a great effect on thedriving performance of the tire. Thus, by the recessed portions 8 beingdensely disposed in the end portion regions ER′ in the tirecircumferential direction of the block 5 of the center land portion 31,the edge components are increased and the effect of improving thedriving performance of the tire provided by the recessed portions 8 issignificantly obtained.

Third Modified Example

FIGS. 25 to 28 are explanatory diagrams illustrating a modified exampleof the pneumatic tire illustrated in FIG. 2. FIG. 25 is a plan view ofthe tread surface of the pneumatic tire 1. FIG. 26 is a plan view of oneof the blocks 5 that compose the shoulder land portion 33. FIG. 27 is aplan view of one of the blocks 5 that compose the second land portion32. FIG. 28 is a plan view of one of the blocks 5 that compose thecenter land portion 31.

In the configuration of FIG. 2, as described above, by disposing theplurality of recessed portions 8 unevenly in the contact patch of oneblock 5, the opening area ratio Se of the recessed portions 8 in the endportion regions ER of one block 5 in the tire lateral direction is madegreater than the opening area ratio Sc of the recessed portions 8 in thecentral portion region in the tire lateral direction (Sc<Se).Specifically, as illustrated in FIGS. 3, 6, and 7, the recessed portions8 are densely disposed in the left and right end portion regions ER, ERof the block 5 in the tire lateral direction. Additionally, the recessedportions 8 of the land portions 31 to 33 have the same opening shape andthe same opening area.

However, the present technology is not limited to such a configuration,and by the plurality of recessed portions 8 having different openingareas in the contact patch of one rib or block, the opening area ratioSe of the recessed portions 8 in the end portion regions of one rib orblock in the tire lateral direction may be made greater than the openingarea ratio Sc of the recessed portions 8 in the central portion regionin the tire lateral direction (Sc<Se). In other words, the recessedportions 8 with a relatively large opening area are disposed in the endportion regions ER in the tire lateral direction.

Specifically, in the configurations of FIGS. 26 to 28, by the averagevalue Ae of the opening area of the recessed portions 8 in the endportion regions ER in the tire lateral direction and the average valueAc of the opening area of the recessed portions 8 in the central portionregion (reference sign is omitted in the drawings) in the tire lateraldirection having the relationship Ac <Ae, the condition Sc<Se for theopening area of the recessed portions 8 is satisfied. Additionally, theaverage values Ae, Ac of the opening area of the recessed portions 8preferably have the relationship 1.5≤Ae/Ac≤4.0, and more preferably therelationship 2.0≤Ae/Ac≤3.0. In a configuration in which all of therecessed portions 8 are disposed in the end portion regions ER, Ac isequal to zero, thus satisfying the conditions Ac<Ae and Sc<Se.

The average values Ac, Ae of the opening area are each calculated as theratio between the sum of the opening area of the recessed portions in apredetermined region and the total number of recessed portions in thepredetermined region.

Additionally, in a configuration in which the land portions are formedby a plurality of blocks arranged in the tire circumferential direction(see FIG. 2), 70% or more, and preferably 80% or more of the blocks 5that compose one row of blocks preferably satisfy the conditions Ac<Aeand Sc<Se for the opening area of the recessed portions 8 describedabove. In the entire tread, it is only required that at least one landportion satisfies the conditions for the row of blocks.

In the configuration described above, the recessed portions 8 with arelatively large opening area are disposed in the end portion regions ERof the blocks 5 where a film of water is likely to form during travel onicy road surfaces. Thus, a film of water on the road contact surfacewith an icy road surface is efficiently absorbed due to the waterabsorbing function provided by the recessed portions 8. As a result, theadhesive properties of the block road contact surface to an icy roadsurface is improved, and the braking performance on ice of the tire isimproved. Additionally, by disposing the recessed portions 8 with arelatively small opening area in the central portion region, the contactpatch area of the central portion region of the block 5 is ensured andthe braking performance on ice of the tire is improved.

For example, in the configuration of FIG. 26, one block 5 of theshoulder land portion 33 includes a total of 16 recessed portions 8 inthe contact patch. Specifically, eight recessed portions 8 areindividually disposed in the end portion regions ER and the centralportion region (reference sign is omitted in the drawings) in the tirelateral direction. The recessed portions 8 have the same opening shape.Additionally, the recessed portions 8 with a relatively large openingarea are disposed in the end portion regions ER, and the recessedportions 8 with a relatively small opening area are disposed in thecentral portion region. As a result, the condition Ac<Ae for the openingarea of the recessed portions 8 and the condition Sc<Se for the openingarea ratio are both satisfied in each region. Additionally, in theshoulder land portion 33, the recessed portions 8 in all of the blocks 5satisfy the conditions Ac<Ae and Sc<Se described above (see FIG. 25).

In the configuration of FIG. 27, one block 5 of the second land portion32 located outward in the tire lateral direction (see FIG. 25) includesa total of 16 recessed portions 8 in the contact patch. Specifically,eight recessed portions 8 are individually disposed in the end portionregions ER and the central portion region (reference sign is omitted inthe drawings) in the tire lateral direction. The recessed portions 8have the same opening shape. Additionally, the recessed portions 8 witha relatively large opening area are disposed in the end portion regionsER, and the recessed portions 8 with a relatively small opening area aredisposed in the central portion region. As a result, the condition Ac<Aefor the opening area of the recessed portions 8 and the condition Sc<Sefor the opening area ratio are both satisfied in each region.Additionally, in the second land portion 32, the recessed portions 8 inall of the blocks 5 satisfy the conditions Ac<Ae and Sc<Se describedabove (see FIG. 25).

Additionally, in the configuration of FIG. 28, one block 5 of the centerland portion 31 includes a total of 37 recessed portions 8 in thecontact patch. Specifically, a total of 18 recessed portions 8 aredisposed in the left and right end portion regions ER in the tirelateral direction and nineteen recessed portions 8 are disposed in thecentral portion region (reference sign is omitted in the drawings) inthe tire lateral direction. The recessed portions 8 have the sameopening shape. Additionally, the recessed portions 8 with a relativelylarge opening area are disposed in the end portion regions ER, and therecessed portions 8 with a relatively small opening area are disposed inthe central portion region. The condition Ac<Ae for the opening area ofthe recessed portions 8 and the condition Sc<Se for the opening arearatio are both satisfied in each region. Additionally, in the centerland portion 31, the recessed portions 8 in all of the blocks 5 satisfythe conditions Ac<Ae and Sc <Se described above (see FIG. 25).

In the configuration described above, 70% or more, and preferably 80% ormore of the recessed portions 8 disposed in the end portion regions ERin the tire lateral direction preferably have an opening area largerthan the average value of the opening area of the recessed portions 8disposed in the block 5. In other words, the majority of the largerrecessed portions 8 are disposed in the end portion regions ER. As aresult, a film of water formed in the end portion regions ER duringtravel on icy road surfaces is efficiently absorbed by the largerrecessed portions 8. For example, in the configurations of FIGS. 25 to28, one block 5 is provided with two types of recessed portions 8 withdiffering opening areas, and all of the recessed portions 8 with thelarger opening area are disposed in the end portion regions ER.Additionally, only the larger recessed portions 8 are disposed in theend portion regions ER, and only the smaller recessed portions 8 aredisposed in the central portion region. As a result, the regions areprovided with recessed portions 8 of different sizes. As a result, adistinctive arrangement pattern of the recessed portions 8 is formed.

However, the present technology is not limited to such a configurationand at least one of the smaller recessed portions may be disposed in theend portion regions ER (not illustrated).

Additionally, in the configuration described above, the recessedportions 8 with an opening area greater than the average value arepreferably disposed on the outermost side of the continuous contactpatch in the tire lateral direction. In other words, the recessedportions 8 with an opening area greater than the average value aredisposed closer to the edge portions of the land portions 31 to 33 thanthe other smaller recessed portion 8. The edge portions of the landportions 31 to 33 are subject to high ground contact pressure and,during travel on icy road surfaces, a film of water is likely to form onthe edge portions. Accordingly, by disposing the larger recessedportions 8 in the edge portions of the land portions 31 to 33, the filmof water on the road contact surface is efficiently absorbed by thelarger recessed portions 8. For example, in the configuration of FIGS.25 to 28, the larger recessed portions 8 are disposed along the edges ofthe block 5 proximal to the circumferential grooves 21 to 23. Thus, thewater absorbing function of the recessed portions 8 is increased.

Additionally, in the configuration described above, the land portions 31to 33 are rows of blocks that include a plurality of blocks 5, andinclude a plurality of sipes 6 and a plurality of types of recessedportion 8 with differing opening areas. The plurality of sipes 6 aredisposed side by side in the tire circumferential direction and dividethe land portions 31 to 33 into a plurality of sections. The recessedportions 8 with an opening area larger than the average value arepreferably disposed in at least one of three sections adjacent in thetire circumferential direction. In other words, three discretionaryadjacent sections defined by the sipes 6 include at least one largerrecessed portion 8. As a result, by the larger recessed portions 8 beingdisposed in a dispersed manner in the tire circumferential direction,during travel on icy road surfaces, a film of water on the road contactsurface is efficiently absorbed. For example, in the configuration ofFIGS. 25 to 28, one or both of two discretionary adjacent sectionsdefined by the sipes 6 include a larger recessed portion 8. Thus, therecessed portions 8 are disposed densely in each section in the tirecircumferential direction.

Additionally, in the configuration described above, the land portions 31to 33 are rows of blocks that include a plurality of block 5, and therecessed portions 8 with an opening area greater than the average valueare preferably disposed in the corner portions of the blocks 5. Thecorner portions of the blocks 5 are subject to high ground contactpressure and, during travel on icy road surfaces, a film of water islikely to form on the edge portions. Accordingly, by disposing therecessed portions 8 in the corner portions of the blocks 5, a film ofwater formed on the road contact surface during travel on icy roadsurfaces is efficiently absorbed. For example, in the configuration ofFIGS. 25 to 28, the larger recessed portions 8 are disposed in all ofthe corner portions of the blocks 5 formed where the circumferentialgrooves 21 to 23 and the lug grooves 41 to 43 meet (see FIG. 25).Furthermore, the larger recessed portions 8 are also disposed in thecorner portions of the notched portions 311 formed in the center landportion 31 (see FIG. 28). Thus, the water absorbing function of therecessed portions 8 is increased.

Note that in the configuration of FIGS. 25 to 28, the disposal number Ncof the recessed portions 8 in the central portion region of each block 5and the disposal number Ne of the recessed portions 8 in the end portionregions ER are substantially the same, and the disposal densities of therecessed portions 8 in the regions are substantially the same.Additionally, the disposal numbers Ne, Nc of the recessed portions 8 ineach region preferably have the relationship 0.90<Ne/Nc<1.10. As aresult, the recessed portions 8 are disposed in the blocks 5 with auniform disposal density.

However, the present technology is not limited to such a configuration,and in addition to the condition Ac<Ae described above, the disposalnumbers Ne, Nc of the recessed portions 8 in each region may have therelationship 1.20≤Ne/Nc, and more preferably the relationship1.50≤Ne/Nc. In other words, in the end portion regions ER in the tirelateral direction, the recessed portions 8 have a relatively largeopening area and are disposed densely. As a result, the ratio Ae/Ac ofthe opening area of the recessed portions 8 in each region can bereduced while the condition Sc<Se for the opening area ratio of therecessed portions 8 in each region can be efficiently adjusted.

Fourth Modified Example

FIGS. 29 to 31 are explanatory diagrams illustrating a modified exampleof the pneumatic tire illustrated in FIG. 25. FIG. 29 is a plan view ofone of the blocks 5 that compose the shoulder land portion 33. FIG. 30is a plan view of one of the blocks 5 that compose the second landportion 32. FIG. 31 is a plan view of one of the blocks 5 that composethe center land portion 31.

In the configuration of FIG. 25, as illustrated in FIGS. 26 to 28described above, the plurality of recessed portions 8 are givendifferent opening areas in the contact patch of one rib or block so thatthe opening area ratio Se of the recessed portions 8 in the end portionregions in the tire lateral direction of one rib or block is greaterthan the opening area ratio Sc of the recessed portions 8 in the centralportion region in the tire lateral direction (Sc<Se).

However, the present technology is not limited to such a configuration,and the plurality of recessed portions 8 may be given different openingareas in the contact patch of one rib or block so that the opening arearatio Se′ of the recessed portions 8 in the end portion regions ER′ inthe tire circumferential direction of one rib or block is greater thanthe opening area ratio Sc′ of the recessed portions 8 in the centralportion region in the tire circumferential direction (Sc′<Se′). In otherwords, the recessed portions 8 with a relatively large opening area aredisposed in the end portion regions ER′ in the tire circumferentialdirection.

Specifically, in the configurations of FIGS. 29 to 31, by the averagevalue Ae′ of the opening area of the recessed portions 8 in the endportion regions ER′ in the tire circumferential direction and theaverage value Ac′ of the opening area of the recessed portions 8 in thecentral portion region (reference sign is omitted in the drawings) inthe tire circumferential direction having the relationship Ac′<Ae′, thecondition Sc′<Se′ for the opening area of the recessed portions 8 issatisfied. Additionally, the average values Ae′, Ac′ of the opening areaof the recessed portions 8 preferably have the relationship1.5<Ae′/Ac′<4.0, and more preferably the relationship 2.0<Ae′/Ac′<3.0.In a configuration in which all of the recessed portions 8 are disposedin the end portion regions ER′, Ac′ is equal to zero, thus satisfyingthe conditions Ac′<Ae′ and Sc′<Se′.

Additionally, in a configuration in which the land portions are formedby a plurality of blocks arranged in the tire circumferential direction(see FIG. 2), 70% or more, and preferably 80% or more of the blocks 5that compose one row of blocks preferably satisfy the conditions Ac′<Ae′and Sc′<Se′ for the opening area of the recessed portions 8 describedabove. In the entire tread, it is only required that at least one landportion satisfies the conditions for the row of blocks.

In the configuration described above, the recessed portions 8 with arelatively large opening area are disposed in the end portion regionsER′ of the blocks 5 where a film of water is likely to form duringtravel on icy road surfaces. Thus, a film of water on the road contactsurface is efficiently absorbed due to the water absorbing functionprovided by the recessed portions 8. As a result, the adhesiveproperties of the block road contact surface to an icy road surface isimproved, and the braking performance on ice of the tire is improved.Additionally, by disposing the recessed portions 8 with a relativelysmall opening area in the central portion region, the contact patch areaof the central portion region of the block 5 is ensured and the brakingperformance on ice of the tire is improved.

For example, in the configuration of FIG. 29, one block 5 of theshoulder land portion 33 includes a total of 16 recessed portions 8 inthe contact patch. Specifically, eight recessed portions 8 areindividually disposed in the end portion regions ER′ and the centralportion region (reference sign is omitted in the drawings) in the tirecircumferential direction. The recessed portions 8 have the same openingshape. Additionally, the recessed portions 8 with a relatively largeopening area are disposed in the end portion regions ER′, and therecessed portions 8 with a relatively small opening area are disposed inthe central portion region. As a result, the condition Ac′<Ae′ for theopening area of the recessed portions 8 and the condition Sc′<Se′ forthe opening area ratio are both satisfied in each region. Additionally,in the entire shoulder land portion 33, the recessed portions 8 in allof the blocks 5 satisfy the conditions Ac′<Ae′ and Sc′<Se′ describedabove.

In the configuration of FIG. 30, one block 5 of the second land portion32 located outward in the tire circumferential direction (see FIG. 25)includes a total of 16 recessed portions 8 in the contact patch.Specifically, eight recessed portions 8 are individually disposed in thefront and back end portion regions ER′ and the central portion region(reference sign is omitted in the drawings) in the tire circumferentialdirection. The recessed portions 8 have the same opening shape.Additionally, the recessed portions 8 with a relatively large openingarea are disposed in the end portion regions ER′, and the recessedportions 8 with a relatively small opening area are disposed in thecentral portion region. As a result, the condition Ac′<Ae′ for theopening area of the recessed portions 8 and the condition Sc′<Se′ forthe opening area ratio are both satisfied in each region. Additionally,in the entire second land portion 32, the recessed portions 8 in all ofthe blocks 5 satisfy the conditions Ac′<Ae′ and Sc′<Se′ described above.

In the configuration of FIG. 31, one block 5 of center land portion 31includes a total of 36 recessed portions 8 in the contact patch.Specifically, 18 recessed portions 8 are individually disposed in thefront and back end portion regions ER′ and the central portion region(reference sign is omitted in the drawings) in the tire circumferentialdirection. The recessed portions 8 have the same opening shape.Additionally, the recessed portions 8 with a relatively large openingarea are disposed in the end portion regions ER′, and the recessedportions 8 with a relatively small opening area are disposed in thecentral portion region. As a result, the condition Ac′<Ae′ for theopening area of the recessed portions 8 and the condition Sc′<Se′ forthe opening area ratio are both satisfied in each region. Additionally,in the entire center land portion 31, the recessed portions 8 in all ofthe blocks 5 satisfy the conditions Ac′<Ae′ and Sc′<Se′ described above.

In the configuration described above, 70% or more, and preferably 80% ormore of the recessed portion 8 disposed in the end portion regions ER′in the tire circumferential direction preferably have an opening arealarger than the average value. In other words, the recessed portions 8with a larger opening area are disposed in the end portion regions ER′.As a result, a film of water formed in the end portion regions ER′during travel on icy road surfaces is efficiently absorbed by the largerrecessed portions 8. For example, in the configurations of FIGS. 29 to31, one block 5 is provided with two types of recessed portions 8 withdiffering opening areas, and all of the recessed portions 8 with thelarger opening area are disposed in the end portion regions ER′.Additionally, only the larger recessed portions 8 are disposed in theend portion regions ER′, and only the smaller recessed portions 8 aredisposed in the central portion region. As a result, the regions areprovided with recessed portions 8 of different sizes. As a result, adistinctive arrangement pattern of the recessed portions 8 is formed.

However, the present technology is not limited to such a configurationand at least one of the smaller recessed portions may be disposed in theend portion regions ER′.

Additionally, in the configuration described above, the recessedportions 8 with an opening area greater than the average value arepreferably disposed on the outermost side of the continuous contactpatch in the tire circumferential direction. In other words, therecessed portions 8 with an opening area greater than the average valueare disposed closer to the edge portions of the land portions 31 to 33than the other smaller recessed portion 8. The edge portions of the landportions 31 to 33 are subject to high ground contact pressure and,during travel on icy road surfaces, a film of water is likely to form onthe edge portions. Accordingly, by disposing the larger recessedportions 8 in the edge portions of the land portions 31 to 33, the filmof water on the road contact surface is efficiently absorbed by thelarger recessed portions 8. For example, in the configuration of FIGS.30, 31, the larger recessed portions 8 are disposed along the edges ofthe block 5 proximal to the lug grooves 41, 42. Thus, the waterabsorbing function of the recessed portions 8 is enhanced.

Additionally, in the configuration described above, the land portions 31to 33 are rows of blocks that include a plurality of blocks 5, and therecessed portions 8 with an opening area greater than the average valueare preferably disposed in the corner portions of the blocks 5. Thecorner portions of the blocks 5 are subject to high ground contactpressure and, during travel on icy road surfaces, a film of water islikely to form on the edge portions. Accordingly, by disposing therecessed portions 8 in the corner portions of the blocks 5, a film ofwater formed on the road contact surface during travel on icy roadsurfaces is efficiently absorbed. For example, in the configuration ofFIGS. 29 to 31, the larger recessed portions 8 are disposed in theblocks 5 in all of the corner portions formed where the circumferentialgrooves 21 to 23 and the lug grooves 41 to 43 meet (see FIG. 25). Thus,the water absorbing function of the recessed portions 8 is enhanced.

Note that in the configuration of FIGS. 29 to 31, the disposal numberNc′ of recessed portions 8 in the central portion region of each block 5and the disposal number Ne′ of the recessed portions 8 in the endportion regions ER′ are substantially the same, and the disposaldensities of the recessed portions 8 in the regions are substantiallythe same. Additionally, the disposal numbers Ne′, Nc′ of the recessedportions 8 in each region preferably have the relationship0.90<Ne′/Nc′<1.10. As a result, the recessed portions 8 are disposed inthe blocks 5 with a uniform disposal density.

However, the present technology is not limited to such a configuration,and in addition to the condition Ac′<Ae′ described above, the disposalnumbers Ne′, Nc′ of the recessed portions 8 in each region may have therelationship 1.20<Ne′/Nc′, and more preferably the relationship1.50<Ne′/Nc′. In other words, in the end portion regions ER in the tirecircumferential direction, the recessed portions 8 have a relativelylarge opening area and are disposed densely. As a result, the ratioAe′/Ac′ of the opening area of the recessed portions 8 in each regioncan be reduced while the condition Sc′<Se′ for the opening area ratio ofthe recessed portions 8 in each region can be efficiently adjusted.

Effects

As described above, the pneumatic tire 1 is provided with, in the treadsurface, the land portions 31 to 33 that include a rib or a plurality ofblocks (see FIGS. 2, 25). The land portions 31 to 33 are provided withthe plurality of narrow shallow grooves 7 and the plurality of recessedportions 8 in the contact patch (see FIGS. 3 and 4). Additionally, theopening area ratio Se of the recessed portions 8 in the end portionregions ER in the tire lateral direction of one continuous contact patchand the opening area ratio Sc of the recessed portions 8 in the centralportion region in the tire lateral direction have the relationshipSc<Se, where the central portion region is defined as the region in thecentral portion in the tire lateral direction occupying 50% of thecontinuous contact patch of the land portions 31 to 33, and the endportion regions are defined as the regions in the left and right endportions in the tire lateral direction occupying 25%.

Such a configuration is advantageous because: (1) by the land portions31 to 33 being provided with recessed portions 8 in the contact patch,the edge components of the land portions 31 to 33 are increased and thebraking performance on ice of the tire is improved; and (2) by theopening area ratio of the recessed portions 8 being greater in the endportion regions ER in the tire lateral direction, the water absorbencyof the road contact surface at the end portion regions ER where a filmof water is likely to form is improved. Such a configuration isbeneficial because the ground contact properties of the end portionregions ER are improved and braking performance on ice of the tire isimproved. Additionally, (3) by the opening area ratio of the recessedportions 8 being smaller in the central portion region in the tirelateral direction, the contact patch area of the central portion regionof the land portions 31 to 33 is ensured, and the braking performance onice of the tire is improved. Additionally, (4) by the recessed portion 8being shallow compared to the sipes (for example a linear sipe 6 or acircular sipe (not illustrated)) the rigidity of the land portions 31 to33 is appropriate ensured. Thus, the braking performance on ice of thetire is ensured.

In the pneumatic tire 1, the opening area ratio Se of the recessedportions 8 in the end portion regions ER in the tire lateral directionand the opening area ratio Sc of the recessed portions 8 in the centralportion region in the tire lateral direction have the relationship1.50<Se/Sc. As a result, the ratio Se/Sc of the opening area ratios ofthe recessed portions 8 in each region is ensured, and the functionprovided by the non-uniform opening area of the recessed portions 8 isappropriately obtained.

Additionally, in the pneumatic tire 1, the disposal number Ne of therecessed portions 8 in the end portion regions ER in the tire lateraldirection and the disposal number Nc of the recessed portions 8 in thecentral portion region in the tire lateral direction have therelationship Nc<Ne (see FIGS. 3, 6, and 7). In such a configuration, bythe recessed portions 8 being disposed densely in the end portionregions ER in the tire lateral direction, the water absorbency of theroad contact surface at the end portion regions ER where a film of wateris likely to form is improved. Such a configuration is beneficialbecause the ground contact properties of the end portion regions ER areimproved and braking performance on ice of the tire is improved.Additionally, by the recessed portions 8 being disposed sparsely in thecentral portion region in the tire lateral direction, the contact patcharea of the central portion region of the land portions 31 to 33 isensured, and the braking performance on ice of the tire is improved.

Additionally, in the pneumatic tire 1, the disposal number Ne of therecessed portions 8 in the end portion regions ER in the tire lateraldirection and the disposal number Nc of the recessed portions 8 in thecentral portion region in the tire lateral direction have therelationship 1.50<Ne/Nc (see FIGS. 3, 6, and 7). Such a configuration isadvantageous because the density of the recessed portions 8 in eachregion is made appropriate, and the function of improving the brakingperformance on ice of the tire is appropriately obtained.

Additionally, in the pneumatic tire 1, the disposal density Da of therecessed portions 8 in the entire region of one continuous contact patchis in the range 0.8 unit/cm²≤Da≤4.0 unit/cm². Such a configuration isadvantageous because the disposal density of the recessed portions 8 ismade appropriate. In other words, by satisfying 0.8 unit/cm²≤Da, thedisposal number of recessed portions 8 is ensured, and the film of waterremoving function of the recessed portion 8 is appropriately ensured.Additionally, by satisfying Da≤4.0 unit/cm², the contact patch area ofthe land portions 31 to 33 is appropriately ensured.

In the pneumatic tire 1, the land portions 31 to 33 include, in thecontact patch, the plurality of sipes 6, and the recessed portions 8 aredisposed spaced apart from the sipes 6 (for example, see FIG. 3). Such aconfiguration is advantageous because by disposing the recessed portions8 and the sipes 6 separate from each other, the rigidity of the landportions 31 to 33 is ensured and the braking performance on ice of thetire is improved.

Additionally, in the pneumatic tire 1, the sipes 6 are disposed side byside in the tire circumferential direction defining the land portions 32into a plurality of sections (for example, see FIG. 6). Additionally,the sections including the recessed portions 8 only in the centralportion region in the tire lateral direction and the sections includingthe recessed portions 8 only in the end portion regions ER in the tirelateral direction are disposed alternately in the tire circumferentialdirection. Such a configuration is advantageous because by disposing therecessed portions 8 in a dispersed manner, the film of water absorbingfunction of the recessed portions 8 can be increased and the rigidity ofthe land portions can be ensured. Additionally, by the consecutivesections including recessed portions, a film of water on the roadcontact surface is efficiently absorbed and the braking performance onice of the tire is improved.

Additionally, in the pneumatic tire 1, the sipes 6 are disposed side byside in the tire circumferential direction to divide each of the landportions 31 to 33 into a plurality of sections. Additionally, at leastone of a discretionary pair of adjacent sections includes a recessedportion 8 in the end portion regions ER in the tire lateral direction(see FIGS. 3 and 7). Such a configuration is advantageous because, bythe recessed portions 8 being disposed densely in the end portionregions ER in the tire lateral direction, a film of water on the roadcontact surface is efficiently absorbed and the braking performance onice of the tire is improved.

Additionally, in the pneumatic tire 1, the sipes 6 are disposed side byside in the tire circumferential direction to divide each of the landportions 31 to 33 into a plurality of sections. Three adjacent sectionsinclude a section including a recessed portion 8 in the end portionregions ER in the tire lateral direction and a section including arecessed portion 8 in the central portion region in the tire lateraldirection (for example, see FIGS. 3 and 6). Such a configuration isadvantageous because the recessed portions 8 are disposed dispersedlythroughout the end portion regions and the central portion region of theland portions 31 to 33.

Additionally, in the pneumatic tire 1, the sipes 6 are disposed side byside in the tire circumferential direction to divide each of the landportions 31 to 33 into a plurality of sections. Three discretionarysections adjacent in the tire circumferential direction include asection including a recessed portion 8 and a section without a recessedportion 8 (see FIG. 7). In such a configuration, by disposing a sectionwithout a recessed portion 8, the recessed portions 8 are disposed in adispersed manner. Such a configuration is advantageous because thecontact patch area of the land portions 31 to 33 is ensured, and thebraking performance on ice of the tire is improved.

Additionally, in the pneumatic tire 1, the land portions 31 to 33 arerows of blocks that each include a plurality of blocks 5, and therecessed portions 8 are disposed in the corner portions of the blocks 5(see FIGS. 3, 6, and 7). In such a configuration, the recessed portions8 are disposed in the corner portions of the blocks 5 where the groundcontact pressure is high and a film of water is likely to form. Such aconfiguration is advantageous because a film of water on the roadcontact surface is efficiently absorbed and the braking performance onice of the tire is improved.

Additionally, in the pneumatic tire 1, the land portions 31 to 33 arerows of blocks that includes a plurality of blocks 5, and the recessedportions 8 are not disposed in the end portions of blocks 5 in the tirecircumferential direction or the central portion region in the tirelateral direction (see FIGS. 3, 6, and 7). Such a configuration isadvantageous because the contact patch area and the rigidity of the endportions of the blocks on the leading side and trailing side areensured, and the braking performance on ice of the tire is improved.

Additionally, in the pneumatic tire 1, the opening area of the recessedportion 8 ranges from 2.5 mm² to 10 mm². Such a configuration isadvantageous because the opening area of the recessed portions 8 is madeappropriate. In other words, by the opening area of the recessedportions 8 being 2.5 mm² or greater, the edge function and the waterabsorbency of the recessed portions 8 are ensured. Additionally, by theopening area of the recessed portions 8 being 10 mm² or less, thecontact patch area and the rigidity of the land portions 31 to 33 areensured.

In the pneumatic tire 1, the recessed portions 8 have a circular (seeFIG. 4) or elliptical shape (not illustrated) in the contact patch ofthe land portions 31 to 33. Such a configuration is advantageous becausecompared to a configuration (not illustrated) in which the recessedportions 8 have a polygonal shape, uneven wear of the contact patch ofthe land portions 31 to 33 can be suppressed.

In the pneumatic tire 1, the wall angle α of the recessed portions 8 isin the range −85 degrees≤α≤95 degrees (see FIG. 5). Such a configurationis advantageous because the edge function of the recessed portions 8 isimproved.

Additionally, in the pneumatic tire 1, the depth Hd of the recessedportions 8 and the groove depth Hg of the narrow shallow grooves 7 havethe relationship 0.5≤Hd/Hg≤1.5 (see FIG. 5). Such a configuration isadvantageous because the depth Hd of the recessed portions 8 is madeappropriate. In other words, by satisfying 0.5≤Hd/Hg, the waterabsorbing function of the recessed portions 8 is ensured. Additionally,by satisfying Hd/Hg≤1.5, a decrease in rigidity of the land portions 31to 33 caused by the recessed portions 8 being too deep relative to thenarrow shallow grooves 7 can be suppressed.

In the pneumatic tire 1, at least one recessed portion 8 is disposed ina position that corresponds to a vent hole of a tire mold (notillustrated). Such a configuration is advantageous because the vent holeis effectively utilized, and the number of unnecessary recesses arereduced in the contact patch of the land portions 31 to 33, which allowsthe contact patch area of the land portions 31 to 33 to be appropriatelyensured.

In the pneumatic tire 1, the average value Ae of the opening area of therecessed portions 8 in the end portion regions ER in the tire lateraldirection and the average value Ac of the opening area of the recessedportions 8 in the central portion region in the tire lateral directionhave the relationship Ac<Ae (see FIGS. 25 to 28). In such aconfiguration, by the recessed portions 8 with a relatively largeopening area being disposed in the end portion regions ER of the blocks5 where a film of water is likely to form during travel on icy roadsurfaces, a film of water on the road contact surface with an icy roadsurface is efficiently absorbed. Such a configuration is advantageousbecause the adhesive properties of the block road contact surface to anicy road surface are improved, and the braking performance on ice of thetire is improved. Additionally, by disposing the recessed portions 8with a relatively small opening area in the central portion region, thecontact patch area of the central portion region of the block 5 isensured and the braking performance on ice of the tire is improved.

In the pneumatic tire 1, the average value Ae of the opening area of therecessed portions 8 in the end portion regions ER in the tire lateraldirection and the average value Ac of the opening area of the recessedportions 8 in the central portion region in the tire lateral directionhave the relationship 1.5≤Ae/Ac≤4.0. Such a configuration isadvantageous because the ratio Ae/Ac of the opening area of the recessedportions 8 in each region is made appropriate. In other words, bysatisfying 1.5≤Ae/Ac, the ratio Ae/Ac of the opening area of therecessed portions 8 in each region is ensured, and the function providedby the recessed portions 8 of improving the braking performance on iceof the tire is appropriately obtained. Additionally, by satisfyingAe/Ac≤4.0, the ratio Ae/Ac of the opening area is kept from beingexcessive, and uneven wear of the blocks 5 is suppressed.

In the pneumatic tire 1, the land portions 31 to 33 include a pluralityof types of recessed portions 8 with differing opening areas, and 70% ormore of the recessed portions 8 disposed in the end portion regions ERin tire lateral direction have an opening area larger than the averagevalue of the opening area of the recessed portions 8 disposed in thecontinuous contact patch (see FIGS. 26 to 28). Such a configuration isadvantageous because a film of water at the end portion regions ER isefficiently absorbed by the larger recessed portions 8, thus the brakingperformance on ice of the tire is improved.

In the pneumatic tire 1, the land portions 31 to 33 include a pluralityof types of recessed portions 8 with differing opening areas, and therecessed portions 8 with a larger opening area than the average value ofthe opening area of the recessed portions 8 disposed in the continuouscontact patch are disposed on the outermost side of the continuouscontact patch in the tire lateral direction (see FIGS. 26 to 28). Such aconfiguration is advantageous because a film of water at the end portionregions ER is efficiently absorbed by the larger recessed portions 8,thus the braking performance on ice of the tire is improved.

Additionally, in the pneumatic tire 1, the land portions 31 to 33include a plurality of sipes 6 and a plurality of types of recessedportion 8 with differing opening areas. The plurality of sipes 6 aredisposed side by side in the tire circumferential direction and dividethe continuous contact patches of the land portions 31 to 33 into aplurality of sections (see FIGS. 26 to 28). The recessed portions 8 withan opening area larger than the average value of the opening area of therecessed portions 8 disposed in the continuous contact patch aredisposed in at least one of three discretionary sections adjacent in thetire circumferential direction. Such a configuration is advantageousbecause by disposing the larger recessed portions 8 in a dispersedmanner in the tire circumferential direction, the function of absorbinga film of water on the road contact surface provided by the recessedportions 8 is appropriately ensured.

Additionally, in the pneumatic tire 1, the land portions 31 to 33 arerows of blocks that each include a plurality of blocks 5 and a pluralityof types of recessed portion 8 with differing opening areas (see FIGS.26 to 28). The recessed portions 8 with an opening area larger than theaverage value of the opening area of the recessed portions 8 disposed inthe continuous contact patch are disposed in the corner portions of theblocks 5. Such a configuration is advantageous because a film of wateron the road contact surface is efficiently absorbed.

The pneumatic tire 1 is provided with, in the tread surface, the landportions 31 to 33 that include a plurality of blocks 5 (see FIG. 2). Theland portions 31 to 33 are provided with the plurality of narrow shallowgrooves 7 and the plurality of recessed portions 8 in the contact patch(see FIG. 4). Additionally, the opening area ratio Se′ of the recessedportions 8 in the end portion regions ER′ in the tire circumferentialdirection of one continuous contact patch and the opening area ratio Sc′of the recessed portions 8 in the central portion region in the tirecircumferential direction have the relationship Sc′<Se′, where thecentral portion region is defined as the region in the central portionin the tire circumferential direction occupying 50% of the continuouscontact patch, and the end portion regions are defined as the regions inthe front and back end portions in the tire circumferential directionoccupying 25% (see FIGS. 22 to 24).

Such a configuration is advantageous because: (1) by the land portions31 to 33 being provided with recessed portions 8 in the contact patch,the edge components of the land portions 31 to 33 are increased and thebraking performance on ice of the tire is improved; and (2) by theopening area ratio of the recessed portions 8 being greater in the endportion regions ER′ in the tire circumferential direction, the waterabsorbency of the road contact surface at the end portion regions ER′where a film of water is likely to form is improved. Such aconfiguration is beneficial because the ground contact properties of theend portion regions ER′ are improved and braking performance on ice ofthe tire is improved. Additionally, (3) by the opening area ratio of therecessed portions 8 being smaller in the central portion region in thetire circumferential direction, the contact patch area of the centralportion region of the land portions 31 to 33 is ensured, and the brakingperformance on ice of the tire is improved. Additionally, (4) by therecessed portion 8 being shallow compared to the sipes (for example alinear sipe 6 or a circular sipe (not illustrated)) the rigidity of theland portions 31 to 33 is appropriate ensured. Thus, the brakingperformance on ice of the tire is ensured.

Additionally, in the pneumatic tire 1, the disposal number Ne′ of therecessed portions 8 in the end portion regions ER′ in the tirecircumferential direction and the disposal number Nc′ of the recessedportions 8 in the central portion region in the tire circumferentialdirection have the relationship Nc′<Ne′ (see FIGS. 22 to 24). In such aconfiguration, by the recessed portions 8 being disposed densely in theend portion regions ER′ in the tire circumferential direction, the waterabsorbency of the road contact surface at the end portion regions ER′where a film of water is likely to form is improved. Such aconfiguration is beneficial because the ground contact properties of theend portion regions ER′ are improved and braking performance on ice ofthe tire is improved. Additionally, by the recessed portions 8 beingdisposed sparsely in the central portion region in the tirecircumferential direction, the contact patch area of the central portionregion of the land portions 31 to 33 is ensured, and the brakingperformance on ice of the tire is improved.

In the pneumatic tire 1, the average value Ae′ of the opening area ofthe recessed portions 8 in the end portion regions ER′ in the tirecircumferential direction and the average value Ac′ of the opening areaof the recessed portions 8 in the central portion region in the tirecircumferential direction have the relationship Ac′<Ae′ (see FIGS. 22 to24). In such a configuration, by the recessed portions 8 with arelatively large opening area being disposed in the end portion regionsER′ of the blocks 5 where a film of water is likely to form duringtravel on icy road surfaces, a film of water on the road contact surfacewith an icy road surface is efficiently absorbed. Such a configurationis advantageous because the adhesive properties of the block roadcontact surface to an icy road surface are improved, and the brakingperformance on ice of the tire is improved. Additionally, by disposingthe recessed portions 8 with a relatively small opening area in thecentral portion region, the contact patch area of the central portionregion of the block 5 is ensured and the braking performance on ice ofthe tire is improved.

Examples

FIGS. 32A-32B include a table showing results 1 of performance testingof pneumatic tires according to the embodiments of the presenttechnology. FIGS. 33A-33B include a table showing results 2 ofperformance testing of pneumatic tires according to the embodiments ofthe present technology.

In the performance testing, a plurality of different test tires wereevaluated for braking performance on ice. The test tires with a tiresize of 195/65R15 were mounted on an applicable rim as defined by JATMA,and an air pressure of 230 kPa and the maximum load as defined by JATMAwere applied to the test tires. Also, the test tires were mounted on atest vehicle, a front-engine front-drive (FF) sedan with an enginedisplacement of 1600 cc.

Evaluations related to braking performance on ice were conducted bydriving the test vehicle on a predetermined icy road surface, andbraking distance from a driving speed of 40 km/h was measured. Then, themeasurement results were expressed as index values with the result ofthe conventional example being defined as the reference (100). In thisevaluation, larger values are preferable.

In reference to FIGS. 32A-32B, the test tires of Examples 1 to 11 havethe configuration illustrated in FIGS. 1 and 2, and the blocks 5 of theland portions 31 to 33 include the sipes 6, the narrow shallow grooves7, and the recessed portions 8. Additionally, as illustrated in FIG. 4,the linear narrow shallow grooves 7 are disposed parallel with eachother at an incline with respect to the tire circumferential directionand penetrate through the blocks 5. The narrow shallow grooves 7 have agroove width and a groove depth of 0.3 mm. All of the recessed portions8 in the tread surface have the same shape and a fixed opening area.Additionally, in all of the blocks 5, the disposal number Ne of therecessed portions 8 in the end portion regions ER in the tire lateraldirection and the disposal number Nc of the recessed portions 8 in thecentral portion region in the tire lateral direction have therelationship Nc<Ne. The disposal density Da and the disposal numberratio Ne/Nc of the recessed portions 8 are the average value of all ofblocks 5 in the tread surface. The opening area ratio Se/Sc of therecessed portions 8 is substantially equal to the disposal number ratioNe/Nc of the recessed portions 8 in each region.

In reference to FIGS. 33A-33B, the test tires of Examples 12 to 22 havethe configuration illustrated in FIGS. 1 and 25, and the blocks 5 of theland portions 31 to 33 include the sipes 6, the narrow shallow grooves7, and the recessed portions 8. Additionally, as illustrated in FIG. 4,the linear narrow shallow grooves 7 are disposed parallel with eachother at an incline with respect to the tire circumferential directionand penetrate through the blocks 5. The narrow shallow grooves 7 have agroove width and a groove depth of 0.3 mm. All of the blocks 5 in thetread surface are provided with two types of a plurality of recessedportions 8 with differing opening areas. All of the recessed portions 8have the same shape. Additionally, the recessed portions 8 with thelarger opening area Ae are disposed in the end portion regions ER of theblocks 5 (see FIGS. 26 to 28), and the recessed portions 8 with thesmaller opening area Ac are disposed in the central portion region ofthe blocks 5. In one of the blocks 5, the disposal number Ne of recessedportions 8 in the end portion regions ER is substantially equal to thedisposal number Nc of recessed portions 8 in the central portion region.As a result, the opening area ratio Se/Sc of the recessed portions issubstantially equal to the opening area ratio Ae/Ac of the larger andsmaller recessed portions 8. The disposal density Da of the recessedportions 8 is the average value of all of blocks 5 in the tread surface.

The test tire according to the conventional example had theconfiguration of Example 2 except that while the blocks 5 include thesipes 6 and the narrow shallow grooves 7, the recessed portions 8 werenot provided.

As shown in the test results, it can be seen that the brakingperformance on ice of the tire is improved in the test tires of Examples1 to 22.

1. A pneumatic tire comprising in a tread surface thereof a land portionthat comprises a plurality of blocks, the land portion comprising in acontact patch thereof a plurality of narrow shallow grooves and aplurality of recessed portions, and an opening area ratio Se′ of therecessed portions in end portion regions in a tire circumferentialdirection of one continuous contact patch and an opening area ratio Sc′of the recessed portions in a central portion region in the tirecircumferential direction having a relationship Sc′<Se′, where thecentral portion region is defined as a region in a central portion inthe tire circumferential direction occupying 50% of the continuouscontact patch, and the end portion regions are defined as regions infront and back end portions in the tire circumferential directionoccupying 25%.
 2. The pneumatic tire according to claim 1, wherein theopening area ratio Se′ of the recessed portions in the end portionregions in the tire circumferential direction and the opening area ratioSc′ of the recessed portions in the central portion region in the tirecircumferential direction have a relationship 1.50≤Se′/Sc′.
 3. Thepneumatic tire according to claim 1, wherein a disposal number Ne′ ofthe recessed portions in the end portion regions in the tirecircumferential direction and a disposal number Nc′ of the recessedportions in the central portion region in the tire circumferentialdirection have a relationship Nc′<Ne′.
 4. The pneumatic tire accordingto claim 3, wherein the disposal number Ne′ of the recessed portions inthe end portion regions in the tire circumferential direction and thedisposal number Nc′ of the recessed portions in the central portionregion in the tire circumferential direction have a relationship1.50≤Ne′/Nc′.
 5. The pneumatic tire according to claim 1, wherein adisposal density Da of the recessed portions in an entire region of theone continuous contact patch is in a range 0.8 unit/cm²≤Da≤4.0 unit/cm².6. The pneumatic tire according to claim 1, wherein the land portioncomprises in the contact patch thereof a plurality of sipes, and therecessed portions are disposed spaced apart from the sipes.
 7. Thepneumatic tire according to claim 1, wherein the land portion is a rowof blocks that comprises a plurality of blocks, and the recessedportions are disposed in corner portions of the blocks.
 8. The pneumatictire according to claim 1, wherein the opening area of the recessedportions ranges from 2.5 mm² to 10 mm².
 9. The pneumatic tire accordingto claim 1 wherein the recessed portions have a circular or ellipticalshape at the contact patch of the land portion.
 10. The pneumatic tireaccording to claim 1, wherein a wall angle α of the recessed portions isin a range −85 degrees≤α≤95 degrees.
 11. The pneumatic tire according toclaim 1, wherein a depth Hd of the recessed portions and a groove depthHg of the narrow shallow grooves have a relationship 0.5≤Hd/Hg≤1.5. 12.The pneumatic tire according to claim 1, wherein at least one of therecessed portions is disposed at a position corresponding to a vent holeof a tire mold.
 13. The pneumatic tire according to claim 1, wherein anaverage value Ae′ of the opening area of the recessed portions in theend portion regions in the tire circumferential direction and an averagevalue Ac′ of the opening area of the recessed portions in the centralportion region in the tire circumferential direction have a relationshipAc′<Ae′.
 14. The pneumatic tire according to claim 13, wherein theaverage value Ae of the opening area of the recessed portions in the endportion regions in the tire circumferential direction and the averagevalue Ac of the opening area of the recessed portions in the centralportion region in the tire circumferential direction have a relationship1.5≤Ae′/Ac′≤4.0.
 15. The pneumatic tire according to claim 13, whereinthe land portion comprises a plurality of types of the recessed portionswith differing opening areas, and 70% or more of the recessed portionsdisposed in the end portion regions in the tire circumferentialdirection have a larger opening area than an average value of theopening area of the recessed portions disposed in the continuous contactpatch.
 16. The pneumatic tire according to claim 13, wherein the landportion comprises a plurality of types of the recessed portions withdiffering opening areas, and the recessed portions with an opening arealarger than the average value of the opening area of the recessedportions disposed in the continuous contact patch are disposed on anoutermost side of the continuous contact patch in the tirecircumferential direction.